Methods and Apparatus For Biological Treatment of Waste Waters

ABSTRACT

In a vertical shaft bioreactor, improved devices and methods are provided for enhanced secondary and/or tertiary treatment of wastewater, including residential, municipal and industrial wastewater. The devices and methods of the invention are useful for enhanced secondary wastewater treatment, including BOD and TSS removal. Tertiary treatment can alternately or additionally be achieved in the bioreactor with nitrification of ammonia, with nitrification and denitrification, and with nitrification, denitrification, and chemical phosphorus removal. A vertical shaft bioreactor is also provided which achieves thermophilic aerobic digestion and pasteurization of sewage sludges, optionally to produce class A biosolids.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application Ser. No.10/848,540, filed May 17, 2004, U.S. patent application Ser. No.10/083,995, filed Feb. 25, 2002, and U.S. Provisional Application No.60/271,201, filed Feb. 23, 2001.

TECHNICAL FIELD

The present invention relates to methods and devices for wastewatertreatment. More specifically, the invention relates to vertical shaftbioreactor wastewater treatment apparatus and methods for operating andconstructing same.

BACKGROUND OF THE INVENTION

High efficiency wastewater treatment has become increasingly importantas the world's population continues to grow. The quantity of waterneeded for human consumption and other uses has increased at a rapidpace, while the amount of naturally available water remains unchanged.The ever-increasing demand for usable, clean water has made reclamationof wastewater an essential component of growth and development of humanpopulations.

In the United States and other developed nations, as existingmetropolitan areas become overcrowded, developers are encouraged orrequired to construct new housing in previously undeveloped areas. Manyof these undeveloped areas lack sufficient water for consumption,irrigation and similar purposes, necessitating reclamation and reuse ofavailable water resources. For development in these areas to besuccessful, sewage from the residential use of water, commonly referredto as wastewater, is therefore a primary target for reclamation.

Residential wastewater has a high water content, but requiressubstantial processing before it can be reused because of the humanwaste and other contaminants mixed with it. To achieve reclamation ofresidential wastewater in many new development areas, isolated fromexisting sewage treatment facilities, on-site wastewater treatment andreclamation is highly advantageous or essential.

A wide variety of different wastewater treatment systems have beenproposed for reclaiming residential sewage and other categories ofwastewater. One such system disclosed in U.S. Pat. No. 2,528,649,incorporates a simple sedimentation tank for separating solid waste, or“sludge”, from wastewater. After sedimentation, the sludge is passed toa digestion system where it is allowed to settle so that clear aqueousliquid separates from the sludge. The clarified liquid is redirectedback to the sedimentation tank. Unfortunately, this system suffers froma number of shortcomings that make it inefficient. In particular, thesystem incorporates a relatively crude sedimentation system that merelyallows the influent sewage to separate and does not aerate or facilitateprocessing of the sewage in any other way.

A number of wastewater treatment processes comprise “biological” systemsutilizing microorganisms contained in an activated biomass, or sludgefor the removal of COD, phosphorous and/or nitrogen from wastewater.These treatment processes typically incorporate multiple treatmentphases or “zones”, namely: (1) a preliminary treatment area; (2) aprimary treatment area; and (3) a secondary treatment area. Preliminarytreatment is primarily concerned with the removal of solid inorganicsfrom untreated wastewater. Typically, this preliminary treatmentencompasses a two-stage treatment process in which the debris is removedby screens and/or settling. Organic matter is carried out in the fluidstream for subsequent treatment. Primary treatment entails a physicalprocess wherein a portion of the organics, including suspended solidssuch as feces, food particles, etc. is removed by flotation orsedimentation. Secondary treatment typically encompasses a biologicaltreatment process where microorganisms are utilized to remove remainingorganics, nitrogen and phosphorous from the wastewater fluid stream.Microorganism growth and metabolic activity are exploited and controlledthrough the use of controlled growth conditions.

In large scale municipal or industrial applications, biologicaltreatment processes typically utilize a basin or other reservoir inwhich the wastewater is mixed with a suspension of biomass/sludge.Subsequent growth and metabolism of the microorganisms, and theresultant treatment of the wastewater, is carried out under aerobicand/or anaerobic/anoxic conditions. In most large scale municipal orindustrial treatment systems, the various components of the treatmentprocess are performed in discrete basins or reactors. As such, there isa continuous flow of the wastewater from one process step to the next.Biomass containing the active microorganisms may be recycled from oneprocess step to another. The conditioning of such biomass to enhancegrowth of particularized subgroups of microorganisms possessing aproclivity for performing a specific type of metabolic process, e.g.phosphate removal, nitrogen removal has been the subject matter ofnumerous patents, including: U.S. Pat. No. 4,056,465; U.S. Pat. No.4,487,697; U.S. Pat. No. 4,568,462; U.S. Pat. No. 5,344,562. Theoptimization of other components or aspects of biological wastewatertreatment has also engendered a variety of patents, including: U.S. Pat.No. 2,788,127; U.S. Pat. No. 2,875,151; U.S. Pat. No. 3,440,669; U.S.Pat. No. 3,543,294; U.S. Pat. No. 4,522,722; U.S. Pat. No. 4,824,572;U.S. Pat. No. 5,290,435; U.S. Pat. No. 5,354,471; U.S. Pat. No.5,395,527; U.S. Pat. No. 5,480,548; U.S. Pat. No. 4,259,182; U.S. Pat.No. 4,780,208; U.S. Pat. No. 5,252,214; U.S. Pat. No. 5,022,993; U.S.Pat. No. 5,342,522; U.S. Pat. No. 3,957,632; U.S. Pat. No. 5,098,572;U.S. Pat. No. 5,290,451; Canadian Patent # 1,064,169; Canadian Patent #1,096,976; Canadian Patent # 1,198,837; Canadian Patent # 1,304,839;Canadian Patent # 1,307,059; Canadian Patent # 2,041,329.

Biological removal of organic carbon, nitrogen and phosphorus compoundsfrom waste water requires attention to special environmental conditionswithin the processing equipment. For instance, for bacteria and othermicrobes to convert organic carbon compounds (measured as BOD) to carbondioxide and water, a well mixed aerobic environment is required.Approximately one pound of oxygen is required for each pound of BODremoved. To convert nitrogen compounds to nitrogen gas and carbondioxide, nitrosomas and nitrobacter operate in an aerobic environmentconsuming inorganic carbon. Approximately 4.6 pounds of oxygen isrequired for each pound of ammonia-N converted to nitrate-N (assumingalkalinity is sufficient). Subsequently, facultative bacteria operate inan anoxic environment consuming organic carbon and liberating nitrogengas. Approximately 2.6 pounds of oxygen is recovered for each pound ofnitrate-N converted to nitrogen gas. To biologically tie up phosphate inthe cell mass, an anaerobic step to produce volatile fatty acids isrequired. This is followed by Poly P microbes consuming large amounts ofphosphorus required to metabolize the volatile fatty acids in an aerobicenvironment thus concentrating the phosphate in the biomass (see, e.g.,Abstract by Dr. W. Wilson Western Canada Water and Wastewater ConferenceCalgary AB. January 2002.)

The combination of these many biological processes ideally results in aBiological Nutrient Removal (BNR) process, sometimes called tertiarytreatment. However, a well-designed tertiary treatment operationrequires coordination and sequencing of a complex assemblage ofcomponents, processes and conditions. Each of the constituent biologicalprocessing steps proceeds at its own rate, with specific environmentalparameters required. Efficient tertiary processing also requires thecorrect amounts of specialty microbes to sustain the microbialpopulations and perform specific processing functions.

Current wastewater treatment systems which attempt to provide tertiarytreatment include Upflow Sludge Bed Filter (USBF), Sequencing BatchReactor (SBR) and Membrane Separation Activated Sludge (MSAS) systems.The Sequencing Batch Reactor (SBR) process is a modification of theconventional activated sludge process. U.S. Pat. No. 5,503,748 disclosesa long vertical shaft aerator applied to the SBR technology. The SBRprocess employs a number of discrete steps, typically comprisingsequential fill, reaction, settlement and decantation of wastewater withbiomass in an enclosed reactor. In the initial step of this process,wastewater is transferred into a reactor containing biomass, andcombined to form a mixed liquor. In the reaction step of the treatmentprocess the microorganisms of the biomass utilize and metabolize and/ortake up the nitrogen, phosphorous and/or organic sources in thewastewater. These latter reactions may be performed under anaerobicconditions, anoxic conditions, aerobic conditions, or a combinationthereof to manipulate organism growth, population dynamics andcontaminant processing. The length of this stage will be dependent onthe waste's characteristic, concentration of the biomass, and otherfactors. Following the reaction cycle, the biomass in the mixed liquoris allowed to settle out. A sludge blanket settles on the bottom of thereactor leaving a treated effluent supernatant. The treated andclarified wastewater (i.e. effluent) is subsequently decanted anddischarged. The reactor vessel is then refilled and the treatmentprocess cycle reinitiated. Thus, the sequencing batch reactor's processis based on discrete operation in time, whereas other wastewatertreatment processes are based on distinct operations in space, e.g., byperformance of different reactions in separate vessels.

A number of additional wastewater treatment designs feature an air-liftreactor, which is a mechanically simple, combined gas-liquid flow devicecharacterized by fluid circulation in a defined cyclic pattern through aset of specifically designed channels. Fluid motion is due to the meandensity difference in an upflow (riser) and downflow (downcomer)sections of the reactor. The air-lift reactor is ordinarily comprised ofdistinct zones with different flow patterns. The riser is typically thezone where the gas is injected creating a fluid density difference,resulting in upward flow of both liquid and gas phases. At the top ofthe reactor, there is a gas-liquid separator section, which is typicallya region of horizontal fluid flow and flow reversal where gas bubblesdisengage from the liquid phase. The downcomer is the zone where thegas-liquid dispersion or degassed liquid ordinarily recirculates to theriser. The downcomer zone exhibits either single-phase, two-phasecocurrent, or two-phase mixed cocurrent-countercurrent downward flow,depending on whether the liquid velocity is greater than the free-risevelocity of the bubbles. The base section at the lower end of the vesselcommunicates the exit of the downcomer to the entrance of the riser.

The air-lift reactor has predominantly been used for microorganismfermentation processes such as the ICI single cell protein production.Nonetheless, a number of systems are known which utilize air-liftreactors for wastewater treatment. Among these examples is the Betzreactor (Gasner, Biotech. Bioeng. 16:1179-1195, 1974), and “deep shaft”bioreactors for effluent treatment (see, e.g., Hines et al., Chem. Eng.Sym. Ser. U.K. 41:D1-D10, 1975).

Following the original development of deep shaft bioreactor technology,recent efforts have led to improvements in long vertical shaftbioreactor systems for wastewater treatment. Among these improvements,U.S. Pat. Nos. 4,279,754, 5,645,726, and 5,650,070 issued to Pollockeach disclose a modified vertical shaft bioreactor system for thetreatment of biodegradable wastewater and/or sludge. Generally, thesevertical shaft bioreactor systems comprises a bioreactor, a solid/liquidseparator and intervening apparatus in communication with the bioreactorand separator. The bioreactor comprises a circulatory system whichincludes two or more vertical, side-by-side or coaxial chambers, adownflow chamber (downcomer) and an upflow chamber (riser). Thesechambers are connected at their upper ends through a surface basin andcommunicate at their lower ends via a common “mix zone” adjacent thelower end of the downcomer.

In addition to the mix zone, these reactors feature a “plug flow zone”located below the mix zone and communicating therewith. As previouslydescribed, the term “plug flow” has referred to a net downward migrationof solid particles from the mix zone toward an effluent outlet locatedat the lower end of the reactor. In one application to sludge digestionthe net downward migration has been reported by Guild et al.(Proceedings WEF conf., Atlanta Ga., October 2001), to include localback mixing only, but over extended periods of operation (e.g., about 16hours), inter-zonal mixing occurs.

The waste-containing liquor (“mixed liquor”) is driven through thecirculating system (i.e., between the downflow and upflow chambers, thesurface basin and the mix zone) by injection of an oxygen-containinggas, usually air, near the bottom of the reactor (e.g., at the mix zoneand plug flow zone). A portion of the circulating flow is directed tothe plug flow zone and is removed at the lower end thereof as effluent.In wastewater treatment reactors, the air is typically injected 5-10feet above the bottom of the reactor and, optionally, immediately belowthe lower end of the downcomer. The deepest air injection point dividesthe plug flow zone into a quasi plug flow zone with localized backmixing above the deepest point of air injection, and a strict plug flowzone with reportedly no mixing below the deepest point of air injection.

At start-up of the bioreactor, air is injected into the riser in thenature of an air lift pump, causing liquor circulation between andthrough the upflow and downflow chambers. Fluid in the downcomer has ahigher density than the liquid-bubble mixture of the riser and therebyprovides a sufficient lifting force to maintain circulation.

Once the bioreactor circulation is thus initiated, all of the airinjection is diverted to the mix zone and/or plug flow zone. The airbubbles that rise out of these zones are trained into the upflow chamberand are excluded from the downflow chamber where the downward flow ofliquor exceeds the rise rate of the bubbles. Dissolved oxygen in thecirculating mixed liquor is the principal reactant in the biochemicaldegradation of the waste. As the liquor ascends in the riser to regionsof lower hydrostatic pressure, this and other dissolved gases separateand form bubbles. When the liquid/bubble mixture from the riser entersthe basin, gas disengagement occurs. To facilitate this purpose, thesurface basin is ordinarily fitted with a horizontal baffle at the topof the upflow chamber to force the mixed liquor to traverse a major partof the basin and release spent gas before re-entering the downflowchamber for further treatment.

U.S. Pat. No. 5,650,070 discloses a process where influent waste wateris introduced at depth into the riser chamber through an upwardlydirected outlet arm of an influent conduit. A zone of turbulence iscreated at the lower end of the downflow chamber by the turn-aroundvelocity head as the circulating flow reverses from downward to upwardflow. This mix zone is not well defined but typically is between 15-25feet deep. A portion of the mixed liquor in the mix zone flowsdownwardly into the top of the plug flow zone in response to an equalamount of treated effluent being removed from the lower end of the plugflow zone into an effluent line, as discussed above. During operation ofthe bioreactor the flow of influent liquor to and effluent liquor fromthe bioreactor are controlled in response to changes in level of liquidin the connecting upper basin.

Reaction between waste, dissolved oxygen, nutrients and biomass(including an active microbial population), substantially takes place inan upper circulating zone of the bioreactor defined by the surfacebasin, the upflow and downflow chambers and the mix zone. The majorityof the contents of the mix zone circulate upwardly into the upflowchamber. In this upflow chamber undissolved gas, mostly nitrogen,expands to help provide the gas lift necessary to drive circulation ofthe liquor in the upper part of the reactor. The spent gas is releasedfrom the liquor as it traverses the horizontal baffle in the surfacebasin. The plug flow zone located below the upper circulating zoneprovides a final treatment or “polish” to the mixed liquor flowingdownward from the mix zone to effluent extraction at the lower end ofthe reactor.

The injected oxygen-containing gas dissolves readily under pressure inthe liquor in the plug flow zone where there is localized back mixingresulting in a slow net downward movement of liquor. Undissolved gas(bubbles) migrate upward to the very turbulent mix zone under pressure.The gas to liquid transfer in this zone is very high, reaching overallreactor oxygen transfer efficiencies in excess of 65%. The products ofthe reaction are carbon dioxide and additional biomass which, incombination with unreacted solid material present in the influentwastewater, forms a sludge (or biosolids).

In addition to aerobic digestion of BOD, it is becoming more and moreimportant to couple biological nutrient removal (BNR) of nitrogen andphosphorous compounds with conventional wastewater treatment. As thedemand for higher quality liquid effluent discharges increase, the needfor technologies as provided by the present invention has becomeincreasingly more compelling. The old Secondary Biological treatmentstandard of 30 mg/L BOD and 30 mg/L TSS is no longer adequate in manyjurisdictions and limits are now often placed on nitrogen and phosphorusas well. Effective removal of these nutrients is essential in view ofexisting and developing environmental laws aimed at preventingeutrophication of natural waters and the attendant ecosystem damagesthat result therefrom.

In basic terms, nitrogen removal is accomplished by converting ammoniacontained in a mixed liquor stream to nitrites and nitrates, in thepresence of oxygen, which is known as an aerobic nitrifying stage.Ammonia conversion to nitrite is carried out by microbes known asNitrosomonas, while the conversion of nitrite to nitrate is accomplishedby Nitrobacters. Nitrate conversion to nitrogen gas occurs in an anoxicdenitrifying stage that takes place in a suspended growth environmentdevoid of dissolved oxygen. Nitrogen, carbon dioxide and water isproduced, with the gas being vented from the system. Nitrification ratescan be optimized by regulating interdependent waste stream parameterssuch as temperature, dissolved oxygen levels (D.O.), pH, solidsretention time (SRT), ammonia concentration and BOD/TKN ratio (TotalKjeldahl Nitrogen, or TKN, is organic nitrogen plus the nitrogen fromammonia and ammonium). Higher temperatures and higher dissolved oxygenlevels tend to promote increased nitrification rates, as does pH levelsin 7.0 to 8.0 range. Sludge retention times of from 3.5 to 5, andpreferably 5-8, days dramatically increase nitrification efficiency,after which time efficiencies tend to remain constant. Increases inammonia concentration increases the nitrification rate but only to amaximum level attainable after which further ammonia concentrationincreases do less to increase the rate of nitrification. Rates have alsobeen shown to be maximized at BOD/TKN ratios of less than 1.0 (see,e.g., Abstract by Dr. W. Wilson, Western Canada Water and Wastewater BNRconference, Calgary AB Canada Jan. 2002]]

Physical/Bio-Chemical phosphorous removal typically requires ananaerobic suspended growth zone at the start of the system, and a sludgefermentation tank to supply volatile fatty acids (VFA's) for the energyneeds of the phosphorous ingesting organisms (Acinetobacters). Recentlyit has been reported that anerobic force mains can generate sufficientvolatile acids to premit substantial biological phosphorus removal.

Refractory treatment and polishing stages may be added to the process,downstream of the final clarification stage. In many waste streams, themajority of organic compounds (80%-90%) are easily biodegraded. Theremaining fraction biodegrade more slowly and are termed “refractory”compounds. Prior art biological nutrient removal designs incorporate asingle sludge and a single clarifier, for example, U.S. Pat. No.3,964,998 to Barnard, but in that case the overall oxidation rate of thesystem has to be reduced to satisfy the slowest compound to oxidize.

Biological nutrient removal (BNR) systems can take various processconfigurations. One such embodiment is the five stage ModifiedBardenpho™ process, which is based upon U.S. Pat. No. 3,964,998 toBarnard. It provides anaerobic, anoxic and aerobic stages for removal ofphosphorous, nitrogen and organic carbon. More than 24 Bardenpho™treatment plants are operational, with most using the five stage processas opposed to the previously designed four stage process. Most of thesefacilities require supplemental chemical addition to meet effluentphosphorous limits of less than 1.0 mg/L. Plants using this processemploy various aeration methods, tank configurations, pumping equipmentand sludge handling methods. WEF Manual of Practice No. 8, “Design ofMunicipal Wastewater Treatment Plants”, Vol. 2, 1991.

In the context of vertical bioreactor technology, Pollock (U.S. Pat. No.5,651,892, issued Jul. 29, 1997, incorporated herein by reference)discloses an innovative process utilizing a vertical bioreactor linkedto a flooded filter via a flotation separator. According to this design,improved reaction rates are achieved by separating the biomass into ahigh rate aerobic organic carbon removal step, followed by an aerobicnitrification step using a separate nitrifying biomass. These steps arethen followed by a high rate denitrification step in an anoxicenvironment created by feeding influent and return mixed liquor oreffluent into that zone to provide a source of organic carbon andconsume the oxygen.

Incorporation of an anaerobic processing step for phosphate removal istypically done in a separate reactor—due to the long fermentation timerequired for volatile fatty acid production. Furthermore, phosphorusremoval in single mixed liquor systems is difficult to implement becausethe phosphate rich biomass produced in the aerobic portion of theprocess should not contact the anaerobic fermentation reactor productdue to the risk of re-solubilizing the entrapped phosphate. In otherinstances, biological phosphorus removal is augmented by addition ofmetal salts such as ferric chloride or alum. These can be added directlyinto the aerobic zone of the reactor to chemically bind the phosphate.

Thus, a variety of treatment systems, including coupled vertical shaftreactors and SBR's, have been successfully used to provide tertiarywastewater treatment. However, these tertiary treatment systems involvea single mixed liquor process wherein all of the specialty microbesinvolved in the process are mixed together. These include autotrophicorganisms that utilize energy from inorganic material (e.g., thenitrifiers Nitrosomonas and Nitrobacters), and heterotrophs whichutilize organic energy sources and include the aerobic BOD removers andthe Acinetobacter biological phosphorous removers (Bio-P organisms).Therefore, in all of these types of systems, the rate of treatment iscontrolled by the slowest performing microbe, usually nitrosomas whichconverts ammonium to nitrite. Due to the slow overall rate of treatment,these single mixed liquor systems are called extended aeration systemsand are quite energy intensive.

Despite the foregoing developments and advancements in wastewatertreatment technologies, there remains an urgent need in the art forimproved wastewater treatment systems that can satisfy a broadened rangeof uses and perform expanded and enhanced functions not satisfied byexisting wastewater treatment systems. For example, there is a longunmet need in the art for a simplified wastewater treatment process andapparatus that provides enhanced biological nutrient removal (BNR) andwhich, in certain embodiments, can produce class A bio-solids requiredfor unrestricted land applications. In addition, there remains anunfulfilled need for wastewater treatment systems and methods thatsatisfy these expanded functions while minimizing the costs andenvironmental impacts that attend conventional wastewater treatmentplant installation and operation.

Surprisingly, the present invention satisfies these needs and fulfillsadditional objects and advantages which will become apparent from thefollowing description and appended drawings.

SUMMARY OF THE INVENTION

The invention satisfies these needs and fulfills additional objects andadvantages by providing an improved vertical shaft bioreactor andrelated methods for wastewater treatment that is adapted, inclusive ofthe optional and secondary features and process steps, to provideenhanced secondary and/or tertiary treatment of wastewater, includingresidential, municipal and industrial wastewater.

The devices of the invention can be constructed, configured withsecondary features, or adjusted, to achieve enhanced secondarywastewater treatment, including a very high degree of BOD and TSSremoval.

The present invention provides devices and methods capable of treatingresidential waste water from a human population of 5,000—in a buildingabout the size of a medium sized bungalow. This result may be achievedby devices and methods that produce recycle quality water, class Abiosolids, and a clean odorless off gas.

Alternately or additionally, enhanced secondary treatment can beachieved in the same bioreactor along with nitrification of ammonia(conversion of ammonia to nitrate).

In other alternate embodiments, enhanced secondary treatment is providedalong with nitrification and denitrification (removal of ammonia andnitrate) in a bioreactor of the invention.

In still other devices and methods of the invention, enhanced secondarywastewater treatment in the bioreactor is accompanied by nitrification,denitrification, and chemical phosphorus removal (tertiary treatment).At lower loading rates, some biological phosphorus removal is expectedin the anerobic primary downflow channel due to the presence of attachedgrowth of anaerobic bacteria and the very slow downward circulation rateachieveable with this invention. Anaerobic biological slime has beenfound growing on the downflow channel wall of a similar reactor, undercertain load conditions.

In yet additional embodiments of the invention, a vertical shaftbioreactor is constructed and employed in novel designs and methods toachieve thermophilic aerobic digestion and pasteurization of sewagesludges, optionally including production of class A biosolids.

Additional embodiments and further detailed aspects of the invention areprovided herein, which are set forth in detail in the followingdescription and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.

FIG. 2 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.This embodiment features a conventional sedimentation clarifier followedby an aerated polishing biofilter followed by an ultra violet lightdisinfection chamber and back wash tank.

FIG. 3 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.This embodiment features an integrated circular sedimentation clarifiersurrounding the circular zone 2 head tank which surrounds the circularzone 1 head tank. All three tanks being concentric with the verticalreactor. A provision is made to return settled activated sludge bygravity to either zone 1 or zone 2.

FIG. 4 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.This embodiment features moving bed media circulating in zone 2 oralternately fixed media suspended in the head tank of zone 2.

FIG. 5 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.This embodiment features a pressurized head tank, an off gas collectormeans, said off gas driving an air lift influent pump required toovercome said head tank pressure, a membrane filtration cartridgeoperating under pressure to separate biomass from liquid and a cleanwater ultraviolet (UV) disinfecting chamber also serving as back washstorage for membrane backwashing.

FIG. 6 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in waste water treatment.This embodiment features an integrated clarifier followed by an aeratedpolishing biofilter followed by an ultra violet light disinfectionchamber and filter back wash tank.

FIG. 7 is a diagrammatic vertical section through one embodiment of abioreactor according to the invention for use in treatment of biosolids.This embodiment features an inter zonal self batching air lock at thebottom of the bioreactor. In this case, zone 2 head tank is concentricand internal to zone 1 head tank.

FIG. 8 is an isometric vertical section through one embodiment of thebioreactor according to the invention for use in waste water treatment.This section shows typical arrangement of various channels and theposition of the aeration distribution header, zone 1 head tank, zone 2head tank and an integral sedimentation clarifier.

FIG. 9 is an isometric vertical section of a portion of reactor internalchannels and downcomer flanged and bolted. This figure shows a downcomerexpansion tool which is used during insertion of the assembly into thereactor casing.

FIG. 10 is a diagrammatic end view of the reactor internal sectionshowing the downcomer and radial baffles. The element in the centerrepresents the expansion tool in its relaxed position. The downcomer isalso in its relaxed position. The removable expansion tool which isoperated by actuation means from the ground level, is inserted in itsrelaxed position during fabrication.

FIG. 11 is a diagrammatic end view of the reactor internal sectionshowing the downcomer forced out of round by the expansion tool. Theradial baffles connected to the downcomer are shown relaxed from thecasing wall, allowing easy insertion.

FIG. 12 provides a graphical representation of the EPA time andtemperature requirements for class A bio-solids.

FIG. 13 provides an exemplary block flow diagram of the presentinvention adapted to produce recycle quality water, Class A bio-solids,and clean odourless off-gas. The following key applies to the FIG. 13:

PRELIMINARY TREATMENT

A Fine screens

B Solids hopper-Screenings and washed grit

C Hyrdaclone degritter

Waste Water BNR Treatment as Described Herein

D Deoxygenation unit [channel 32+40]

E Denitrification [head tank 16]

F Anoxic/anaerobic unit [channel 12]

G Aerobic unit [zone 1 channel 80]

H Nitrification [zone 2 head tank, 110 and 82]

I Sedimentation clarifier [120]

J Waste activated sludge float thickener

K Alum or ferric chloride feeder

L Process air compressor

Recycle Quality Water [Units Required by Law]

M Flocculating tank

N Cloth disk filter

O Chlorination

P Ultraviolet disinfection

Q Backwash pump

Thermophilic Aerobic Digestion as Described Herein

Class A Biosolids

R Zone 1 thermophilic aerobic digester

S Zone 2

T Acid feeder

U Polymer feeder

V Centrifuge de-watering

W Flotation cell

X Air compressor

Y Off gas collection system

Z Class A bio-solids collection

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

As illustrated in the attached Figures, the instant invention provides along vertical shaft bioreactor 10 for wastewater treatment. Thebioreactor of the invention shares a number of structural and functionalcharacteristics with previously described vertical shaft bioreactorsystems (see, e.g., U.S. Pat. Nos. 4,279,754, 5,645,726, and 5,650,070issued to Pollock, each incorporated herein by reference), but departsin several important and novel aspects therefrom.

In reference to FIG. 1, the vertical shaft bioreactor 10 of theinvention features a wastewater circulation system which includes two ormore substantially vertical channels, including at least one downflowchannel, or downcomer channel 12, fluidly interconnected in acircuitous, open or closed, path with at least one upflow channel, orriser channel 14. The downcomer and riser channels are typicallyinterconnected at their upper ends via a surface basin or head tank 16,which may be open or closed, and at a lower junction corresponding to amix zone 18 situated below a lower port or aperture 20 of the downcomer.

The downcomer 12 and riser 14 channels are typically defined by separateconduits, for example by separate, cylindrical-walled pipes.Alternatively, they may be defined as interconnected compartments orchannels sharing one or more walls, for example as parallel channelsseparated by partitioning structures (e.g., radial partitions or septa)within an elongate, compartmentalized reactor vessel or frame. Thedowncomer and riser channels are preferably oriented substantiallyparallel to one another, for example in a side-by-side or coaxialrelative configuration.

Typically, the downcomer 12 and riser 14 channels are defined asseparate conduits over at least a portion of their lengths. In oneexample, the downcomer channel is defined by a separate,cylindrical-walled downcomer conduit (e.g., a steel pipe) 22 nestedcoaxially within a larger diameter, cylindrical walled riser conduit 24(which will often correspond to an outer wall or casing of the entirebioreactor assembly). As such, the attached Figures are generally to beinterpreted as schematic illustrations, wherein for ease of illustrationthe drawings which show the downcomer conduit laterally displacedrelative to the riser conduit are intended also to schematicallyillustrate an alternative, parallel or coaxially nested configuration ofthe downcomer conduit within the larger riser conduit.

In one embodiment of the invention adapted for residential use, thewastewater treatment bioreactor 10 of the invention is constructed toservice a small residential community of about 5,000 population.Typically, two parallel bioreactors are installed in accordance with EPAredundancy requirements, in vertical in-ground shafts bored usingconventional drilling technology. In various embodiments, the bioreactorof the invention can be constructed, configured with secondary features,or adjusted to provide the secondary and/or tertiary levels oftreatment, listed below.

a) Secondary treatment (BOD and TSS removal) only.

b) Secondary treatment with nitrification of ammonia (conversion ofammonia to nitrate).

c) Secondary treatment with nitrification and denitrification (removalof ammonia and nitrate).

d) Secondary treatment with nitrification, denitrification, and chemicalphosphorus removed (tertiary treatment). Some biological phosphorusremoval will occur at low loads.

e) Thermophilic aerobic digestion and pasteurization of sewage sludgesto produce class A biosolids.

In brief reference to the following description, the secondary treatmentof a) above may be completely aerobic both in the zone 1 head tank 16and downcomer channel 12 of zone 1, and in the zone 2 upflow channel(s)82 and head tank 15. This configuration requires a shaft of about 30inches diameter and 250 ft. deep, a zone 1 head tank of about 6 ft.diameter×10 ft. deep and a concentric zone 2 head tank of about 12 ft.diameter×10 ft. deep. The concentric clarifier is about 28 ft.diameter×10 ft. deep and is fitted with a rake mechanism to assist insludge removal. In more detailed embodiments, this reactor will treatresidential sewage from at least a 2,500 member human population andproduce <30 mg/L TBOD and <30 mg/L TSS.

The secondary treatment process of b) is also completely aerobic and ofthe same general dimensions as a) except the zone 2 head tank is about16 ft. in diameter. A larger portion of the air originating at thebottom of zone 1 is diverted into zone 2 using a diverter mechanism 84.The treatment system of c) above is designed for anoxic conditions inthe head tank and downcomer of zone 1. In certain embodiments, thisreactor will treat residential sewage from at least a 2,500 member humanpopulation and produce <1 mg/L ammonia-N, <15 mg/L TBOD, and <15 mg/LTSS.

Only a small fraction of air from the lower portion of zone 1 isdiverted into the zone 1 upflow channel(s) 40. In addition to rawinfluent feed in the upper end of zone 1, recycled nitrified effluent orreturn activated sludge from the clarifier or, alternatively from zone 2head tank, is added to the raw influent to create the anoxic conditions.

In this treatment process the reactor is enlarged to approximately 36inches in diameter, zone 1 head tank is increased to about 8 ft.diameter, zone 2 head tank is increased to about 16 ft. in diameter. Theconcentric clarifier has an outside diameter of about 30′ and is fittedwith a rake mechanism. In more detailed embodiments, this process willtreat residential sewage from a human population of 2,500 or greater to<5 mg/L TKN, <10 mg/L TBOD, and <10 mg/L TSS.

The treatment system of d) above is the same general dimension of c).Within the treatment process of d), alum of ferric chloride may be addedinto zone 2 for chemical precipitation of phosphorus. It is usuallyuneconomic to use only a biological phosphorus removal process alone toachieve a high degree of phosphorus removal (e.g., 2-3 mg/L residual) onsmall plants, since a pre-fermentation step to produce volatile fattyacids (VFA) may be required. Typical characteristics of effluent fromthis plant are: TBOD<10 mg/L; TSS<10 mg/L; TN<5 mg/L; PO4<1 mg/L.

In the case of sludge treatment e), the reactor is reconfigured suchthat zone 1 surrounds zone 2, or may be adjacent to zone 2 throughoutthe major portion of the reactor length and zone 2 head tank 15′surrounds the zone 1 head tank 16′. Zone 1 and zone 2 are hydraulicallyconnected at the bottom of zone 2 through a self batching air lockdevice which precludes zone 1 contents from entering zone 2 whileprocessing each batch. The thermophilic aerobic digester volume ofconfiguration e) is about one half the volume of the wastewatertreatment reactor producing the biomass. Because sludge storageprovision is more economic to build than redundancy in reactors, onlyone digester is required for two treatment reactors. Accordingly thesmall town of about 5000 people requires 2 treatment reactors and 1sludge digester all of the same size. The foregoing example is a typicaldesign for small communities of about 5000 people.

Since about 80% of the voidage (air lift) occurs in the top 80-100 ft.of any air lift reactor, the superior channels can be effective between150 and 50 feet deep, preferably 80-88 ft. which is the standard lengthof two joints of double random length pipe. Off the shelf aircompressors are readily available in 100, 125 and 150 psi modelscorresponds to shaft depth of 200, 250 and 300 ft. Although airliftbioreactors have been built between 60 ft. and 500 ft. depths, a morecommon range is 150 to 350 ft. depth and a range of 200 ft. to 300 ft.is now most common.

Conventional water well rigs can drill holes up to about 48 inches anddeep foundation equipment for pilings can drill up to about ten feet indiameter. Augers (where geology permits) can drill up to about 20-ft.diameter but are limited to about 200-ft. depth. Mined shafts can be upto 30 ft. diameter and of virtually any depth.

Small municipal plant reactors (5000 population) will typically beplaced with conventional water well rigs and preferably be about 24 to48 inches in diameter.

Larger communities (10,000-50,000 population) may require shafts of 5 to10 ft. diameter×200 ft. depth placed by deep foundation piling machinesand augers, whereas very large industrial plants (e.g. pulp mills) mayrequire shafts placed by mining techniques.

The long vertical shaft bioreactor 10 of the invention receivesinfluent, typically wastewater or sludge, through an influent conduit 30which introduces the influent into an influent channel 32. The influentflows downward to the bottom of the influent channel, where it exitsthrough a shielded influent port 34 and combines with upflow in a zone 1upflow channel 40 delineated at its lower end by the influent port. Theinfluent port is upturned or otherwise shielded to prevent admission ofbubbles from below the zone 1 upflow channel from entering the influentchannel.

In alternate embodiments of the invention, the influent channel 32 canoptionally accept recycle flow of liquor from the head tank 16 portionof zone 1 of the bioreactor 10. This flow is regulated by a zone 1recycle flow regulator 50, for example a manual or motor-actuatedbaffle, valve or other flow-regulating apparatus. In this context, theinfluent flow through the zone 1 recycle regulator 50 is ordinarilythrottled via an influent flow throttling control mechanism. This caninclude, for example, a system control unit 51 (e.g., a system controlmicroprocessor) operatively linked to a valve or baffle actuator 52 andan optional flow sensor 53 or 53′ for determining influent and/or zone 1recycle flow or alternatively dissolved oxygen DO probe 49 to monitoroxygen levels. Control of influent flow through the regulator functionsin part to adjust the air lift in zone 1 upflow channel 40 andfacilitate gravity influent flow. The combined flow in the zone 1 upflowchannel contains some anoxic air bubbles (see below) and is thereforelighter than the fluid in influent channel 32, and rises. By anoxic airbubbles is meant bubbles predominately containing gasses other thanuseable oxygen. Flow in the zone 1 upflow channel 40 traverses ahorizontal degas plate 54 and descends substantially free of entrainedbubbles in the downcomer channel 12 under gravity and enters the mainriser channel 14 in the vicinity of the mix zone 18, where it isintensively aerated.

At start up of the bioreactor 10, compressed air or otheroxygen-containing gas or, alternatively, a liquid/gas solution orsuspension, is delivered to a lower segment of the reactor to serve asan oxygenation source for aerobic waste processing in the bioreactor.Typically, compressed air is delivered to a sparger or air distributionheader 60 anchored near the bottom of the riser channel 14 below thelower port of the downcomer channel 12 that serves to deliver theprocess air in a substantially dispersed array. Typically, thedistribution header is flat topped or cone shaped with an optional,serrated skirt fixed to the perimeter underside. The header serves todisperse the process air in a substantially uniform, circular array ofair bubbles that emerge as a rising curtain of bubbles from around theperiphery of the header—below the lower port 20 of the downcomer channeland surrounding the mix zone 18. The mix zone is thus generally definedin one embodiment of the invention as the lower portion of the riserchannel below and surrounding the lower port of the downcomer channeland above and surrounding the air distribution header. The flow from thedowncomer channel impinges on an upper surface 61 of the distributionheader and is partially deflected upward. At the same time, bubblesreleased from the periphery of the header mix with the flow from thedowncomer channel and contribute to turbulent mixing of this material,which thereby becomes less dense as a fluid-bubble mixture than thefluid in the downcomer charmer. Accordingly, the resultant fluid-bubblemixture rises within the riser channel 14 to establish circulation inthis portion of the bioreactor having the general circulatory patternindicated by the arrows in FIG. 1.

The compressed air or other oxygen-containing gas or liquid serving asthe oxygenation source for the bioreactor 10 is typically deliveredthrough one or more dedicated oxygenating lines, typically compressedair lines 62. A dedicated compressed air line is connected to acompressed air supply at the surface and runs downward parallel to theriser channel (e.g., nested within the riser conduit 24) extending to anoxygenation port, typically an air delivery port 64, that opens in fluidconnection with the riser channel 14. The air delivery port 64 isgenerally positioned beneath the air distribution header 60 to releasethe compressed air for dispersal by the header, as described above.Within certain embodiments of the invention, compressed air (or otheroxygen-containing gas or liquid) is optionally, or additionally,delivered within the bioreactor by a dual-service aeration/solidsextraction line 66. Functioning of this line can be controlled, e.g., bya system control unit 51 as described above, to optionally delivercompressed air or other oxygen-containing gas or liquid and, in a secondoperation mode, serve as a waste solids extraction line 66 to purgewaste solids from a sump 67 portion of the reactor located at the bottomof the riser channel. The waste solids extraction line extends from thesurface (e.g., from a surface-located, waste-solids extraction/flotationreservoir) to a aeration/waste solids extraction port 68 opening influid connection with the sump. Solid particles that settle into thesump will accumulate over a period of hours of operation. For themajority of the bioreactor's operation time, the aeration/solidsextraction line is continuously purged by flow of compressed air, andtherefore the sump 67 is substantially mixed and aerated and forms afunctional part of the mix zone 18. Periodically, theaeration/extraction line can be depressurized, whereby settled solidswithin the sump will rush to the top of the reactor to be purgedtherefrom. These solids are highly aerated, well stabilized (odor free)and because of the high gas content will spontaneously float to athickened sludge.

In related embodiments of the invention, the improved vertical shaftbioreactor 10 features two simultaneously-operating aeration lines orports to enhance the formation of small, dispersed bubbles to generateupflow currents and supply process air within the bioreactor. The use oftwo aeration lines is exemplified by the dedicated compressed air line62 and dual-function aeration/solids extraction line 66, which eachoperate at least for a majority of the bioreactor process time in acompressed air delivery mode. In this mode, the two lines in concertprovide a cooperative, multiple source compressed air injectionmechanism of the invention, which serves to enhance the turbulence andsmall bubble-forming capacity within the mixing zone 18 of the reactor,which is in turn expanded by the cooperation of multiple compressedaeration lines or ports. In one aspect of this enhanced mixing/bubbleforming mechanism, a first aeration line opening, exemplified by the airdelivery port 64 of dedicated air line 62, is positioned below the airdistribution header 60 and above a second aeration line opening,exemplified by aeration/extraction port 68 of the dual-functionaeration/solids extraction line. Compressed air released from this loweraeration port stimulates fluid mixing and bubble formation near thebottom of the riser channel 14 to set up a first circulation path orvector. The resultant circulating fluid-bubble mixture impinges upwardlyand/or transversely against mixed fluid and bubbles generated by theintroduction of compressed air from the first, upper air line 62. Thisresults in increased shear forces and the production of smaller airbubbles in an enlarged mixing zone, compared to the results achieved byoperation of a single aeration line (see, FIG. 1).

In conjunction with the above-described use of a cooperative, multiplesource compressed air circulation regime, certain embodiments of theinvention incorporate a modified (typically stepped, chambered, orbaffled) header, or a multi-component header complex, to augment theenhanced mixing/bubble forming mechanism provided by multiple,interactive aeration sources. In one aspect, a second, cooperating shearheader 70 is mounted within the riser chamber 14 below the main bubbledistribution header 60 and works in conjunction with two, verticallytiered aeration sources generally as described above. The shear headercan be any flow diverting or channeling device that enhances an upwardand/or transverse or radial flow component within the mixing zonegenerated by a second, lower-positioned aeration source (exemplified bythe aeration/solids extraction port 68). In one exemplary embodiment,the shear header comprises an internally stepped draught tube (FIG. 1)attached by vertical struts to the underside of the distribution header.Compressed air fed into the aeration/solids extraction line 66 causes anair lift effect in the stepped draught tube, thus establishing aseparate circulation pattern or vector in the lower portion of the mixzone as shown in FIG. 1. This upward and/or transverse or radialcirculating flow impinges against mixed fluid and bubbles generated bythe introduction of compressed air from the first, upper air line 62near the perimeter of the distribution header, which interaction isregulated in part by air delivered though the aeration/solids extractionport, while the balance of process air is delivered though the dedicatedair delivery port 64. This creates very high flow rates inside theserrated skirt in increased shear at the perimeter of the distributionheader which aids substantially in shearing bubbles to a smaller size.Whereas previous bioreactors typically generate bubbles at the site ofdistribution in the range of about a half inch to three quarters of aninch in diameter, the novel interactive flow mechanism and cooperativeheader design of the invention generates substantially smaller bubbles,typically about one quarter to one half inch, often less than onequarter inch, down to as small as one-fifth to one-eighth inch or lessin diameter. For example, studies published in the water EnvironmentResearch Journal May/June 1999 pgs. 307-315 (incorporated herein byreference) determined that bubbles about 2 mm are the optimum diameterfor mixing and oxygen transfer. However bubbles of this size do not formnaturally at an orifice without some mechanism for shearing the bubble.The bubble size is determined when the buoyancy force equals theattraction forces at the orifice and bubble size is not necessarily afunction of orifice size. Since bubbles of this size range have a riserate of about 0.8-1.0 ft./sec. in water, a downward circulation velocityof greater than 1 ft./sec. in the vicinity of the serrated skirt 60 willcause the bubble to be sheared from the orifice. The circulationvelocity is regulated by the amount of air injected in line 68 and canbe adjusted independently of the air being applied at orifice 64.Samples extracted periodically in line 66 can be measured for dissolvedoxygen. The circulation velocity between aerator elements 60 and 70 canbe adjusted to maximize the oxygen transfer. This novel design providesenhanced mixing and bubble distribution without unacceptable risk ofclogging. When the aeration/solids extraction line is being used forbiomass wasting, air-flow in the dedicated air line maintains reactorcirculation. At this point, when the aerator barrel of the shear headeris depressurized a new batch of waste biomass transfers from the mixzone 18 to the sump and aeration of biomass within the aeration barrelof the shear header begins again.

Yet additional embodiments of the invention are distinguished by virtueof their novel features for channeling, circulating, and segregatingfluid, air and/or biomass within the reactor 10. These features are inturn variable, combinable in alternative reactor configurations, and/oradjustable within additional aspects of the invention—allowing use ormodification of the reactor for different wastewater treatmentapplications and results. In general aspects, the bioreactor of theinvention features a first treatment or processing “zone” designatedzone 1, wherein the majority (e.g., greater than 80%, up to 90-95% orgreater) of the primary reaction between waste, dissolved oxygen,nutrients and biomass (including an active microbial population), takesplace. Within certain embodiments, this zone is defined to include anupper circulating zone of the bioreactor comprising the surface basin orhead tank 16, a primary reaction chamber 80 comprising a central volumeof the riser channel 14, the downcomer channel 12, and the mix zone 18.

The majority of the contents of the mix zone 18 represent a fluid-bubblemixture that is less dense than the fluid in the downcomer channel 12and therefore circulates upwardly from the mix zone into the primaryreaction chamber 80. Undissolved gas, mostly nitrogen, expands to helpprovide the gas lift necessary to drive circulation of the liquor in theupper part of the reactor 10 in the patterns as shown by the arrowsthroughout the Figures. The products of this primary reaction are carbondioxide and additional biomass which, in combination with unreactedsolid material present in the influent wastewater, forms a sludge (orbiosolids).

In certain embodiments of the invention, as illustrated in FIG. 1,upflow of fluid in the primary reactor channel 80 is segregated intomultiple, smaller upflow channels in an upper section of the bioreactor10. In one exemplary embodiment, upflow from the primary reactor channelis diverted into at least two discrete superior upflow channels, asexemplified by the zone 1 upflow channel 40 and a zone 2 (typicallyoperated as a polishing zone) upflow channel 82 depicted in FIG. 1. Inone exemplary construction design, flow diversion from the primaryreactor channel into multiple, superior channels is achieved byemploying a fixed or adjustable diversion plate 84 or comparable flowdiverting device that is anchored near the top of the primary reactorchannel

The diversion plate 84 is configured and dimensioned to segregate theprimary reactor channel 80 upflow into multiple superior channels.Typically, the diverter plate is configured and dimensioned to interceptand divert a larger fraction of total upflow volume of the fluid-bubblemixture from the primary reactor channel into a selected “aerobic”upflow channel, depending on the desired mode of operation of thebioreacter 10, as further explained below. In the exemplary embodimentshown in FIG. 1, the diverter plate features a vertical baffle 86 thatfacilitates segregation and channeling of the fluid-bubble mixtureflowing upward in the primary reactor channel toward an upwardly angled,laterally or radially extending flow diverting extension 88 of thediverter plate that diverts a larger fraction of the total upflow volumeof fluid and bubbles from the primary reactor channel into one or theother of the first zone upflow channel 40, or second zone upflow channel82. Accordingly, a smaller fraction of the total upflow volume of fluidand bubbles is allowed to pass into the remaining superior upflowchannel 40, thereby limiting as a primary process determinant the flowof aerated fluid into this remaining channel so as to contribute togeneration of anoxic conditions in this channel, if desired.

Selection, positioning and adjustment of the flow diverter mechanismdepends on the selected mode of operation of the bioreacter 10. Inalternative embodiments, the diverter plate 84 can be positioned,shaped, dimensioned and/or adjusted to channel upflow of thefluid-bubble mixture from the primary reactor channel 80 into one ormore superior channels to achieve higher aerobic environmentalconditions in the selected channel(s), while limiting the upflow(particularly of high oxygen-containing fluid) into one or more superiorchannels selected for lower aerobic, even anoxic, environmentalconditions. By way of example, the following steady state functionalityof adjustable baffles 86 and 84 is described. In FIG. 1, 10 bubbles aredepicted as rising uniformly at the top of zone 1 immediately belowbaffle 86. The baffle is adjusted so that 3 bubbles are segregated intoarea 39 and 7 are segregated into area 81. However the flow into area 81is approximately equal to Q, influent/effluent flow+1.75 Q nitratedrecycle flow=2.75 Q. In this exemplary design, the flow into area 39 iscontrolled to 5 Q. Therefore the flow per bubble in area 39 is 5/3=1.7Q/bubble and in area 81 it is 2.75/7=0.4 Q/bubble. Similarly the oxygendemand and supply in the superior channels and head tanks can becalculated. Typically the average BOD in the area 39 and 81 is about 10mg/L and the average ammonia-N concentration to be removed is 15 mg/L(after ammonia used in cell synthesis) and the denitrified recycle flowis 1.75 Q. Therefore the average ammonia concentration would be15/1.75=8.57 mg/L. This level of ammonia-N is equal to 8.75 mg/L-Nx 4.6# oxygen/# N=39 mg/L of BOD equivalent. The total load into zone 2 istherefore=2.75 Q [10+39]=134 Q oxygen units. Since there are 7 bubbleoxygen units the load per bubble is 134/7=19 oxygen unitsrequired/bubble. Similarly the load into area 39 is 5 Q×10 mg/L BOD=50 Qoxygen units required. However in channel 40 above port 34 the loadincreases to 50 Qunits+Q×200 units (assuming the influent BOD is 200mg/L) for a total load of 250 Q units of oxygen required. Since thereare only 3 bubble oxygen units available, the oxygen required per bubbleis 250/3=83 oxygen units. Therefore the oxygen demand per bubble oxygenunit is higher in head tank 16 than in head tank 15 by 83/19=4.3 times.Consequently, if there is measurable dissolved oxygen in head tank 16there will be surplus DO in head tank 15, and if there is surplus DO inhead tank 16 there will substantially more DO at any level below baffle86 down to the mix zone 18. Thus baffle 86 can be adjusted toaccommodate a wide range of load and flow criteria.

Thus, in one aspect of the invention, the improved long vertical shaftbioreactor functions for multi-purpose waste treatment by providingaerobic digestion of BOD as well as single mixed liquor processing BNRtreatment. Referring to FIG. 2, the flow diverter 84 is constructed andconfigured as shown (compare alternate diverter configuration/settingshown by phantom line 90) to divert a majority fraction of total upflowvolume of the fluid-bubble mixture from the primary reactor channel intothe zone 2 upflow channel 82, while limiting the upflow volume of fluidand bubbles from the primary reactor channel 80 into the zone 1 upflowchannel 40. Volume ratio in influent channel 32 and flow down and intothe zone 1 upflow channel (which intercepts only a small fraction of thebubbles from the primary reactor channel) can be finely controlled.Thus, a relatively small amount of air lift and a slow circulation ratecan be provided the zone 1 upflow channel compared to the lift andcirculation in the zone 2 upflow channel in this diverter configuration.The residence time of the fluid mixture in the zone 1 upflow channel istherefore increased, and the oxygen transfer capability in zone 1 upflowchannel 40 is reduced due to the reduced bubble upflow. Notably, thebubbles in the zone 1 upflow channel are mostly nitrogen, because theoxygen is largely consumed in the lower and middle part of zone 1(particularly including the mix zone 18 and the primary reactor channel80 below the diverter).

Within this embodiment and adjustment/operation mode of the bioreactor10, the superior channel referred to as the zone 1 upflow channel 40,can be selected to provide an anoxic environment, achieved in part bythe low relative influx of oxygen and the high oxygen demand of the rawinfluent stream. This anoxic zone continues throughout the circulationpath between the zone 1 upflow channel and the downcomer channel 12, asapproximately indicated by the arrows in FIG. 2. Within this anoxiczone, a final step of BNR processing, denitrification of nitrateinitially contained in the mixture of fluid in the zone 1 upflowchannel, occurs. When this mixture, following the path indicated,reaches the mix zone 18, re-aeration of the anoxic flow exiting thelower downcomer port 20 occurs, and residual BOD that was not removed inthe anoxic zone is oxidized in the lower part of zone 1 (including themix zone and primary reactor channel 80). Thereafter, a portion of theuprising flow in the primary reactor channel flows upward into the zone1 upflow channel 40, because this top portion of zone 1 is designed tobe anoxic, the number of bubbles required for bio-oxidation is reduced.The airlift effect is also greatly reduced to slow the upflow in thispart of the reactor. In addition, the ability to control influent flowvia the zone 1 recycle flow regulator 50 also allows adjustment of airlift and flow in the zone 1 upflow channel.

Within the foregoing operation mode of the bioreactor 10, a majorportion of the uprising air flow in the primary reactor channel 80 flowsupward into the other superior upflow channel(s), exemplified by thezone 2 upflow channel 82. The relative lower liquid upflow fraction thussegregated includes the majority of bubbles originating at the lower endof zone 1 (e.g., bubbles generated by the dedicated air line 62 andoptional multi-purpose aeration/waste solid extraction line 66,functioning in concert with the bubble distribution header 60 andoptional shearing enhancer mechanism exemplified by the shear header70). This active, fluid-bubble mixture segregated into zone 2 byoperation of the diverter 84 enters the zone 2 upflow channel, thenmixes with vigorous re-circulating flow entering zone 2 through a zone 2recirculation channel 110 (which recycles liquor from the zone 2 headtank 15). This recirculation flow is optionally regulated by a zone 2recirculation flow regulator 112, for example a manual or motor-actuatedbaffle, valve or other flow-regulating apparatus. This recycle flowregulator is also optionally controlled by the system control unit 51(e.g., system control microprocessor) operatively linked to a valve orbaffle actuator 52 and optional flow sensor 53 for determining zone 2recycle flow).

When the bioreactor 10 is thus configured and/or adjusted for BNRremoval, nitrification of mixed liquor can be efficiently conducted andcontrolled within zone 2 of the bioreactor, in accordance with theabove-described construction and operation details. Some of the mixedliquor from zone 2 may be discharged to a detached 120 or integrated120′ solids-liquid separator (clarifier) (see, e.g., FIGS. 2-4, and 6).Some of the mixed liquor from zone 2 may be returned to the influentchannel 32, where it undergoes de-nitrification, as described above, andthe cycle repeats. Optionally, some clarified effluent may be returnedto channel 32 during low flow periods, thereby removing more nitrogencompounds overall.

In more detailed embodiments of the invention, influent, returnclarified effluent (e.g., recycled from a separate clarifier 120 orintegrated clarifier 120′), and return activated sludge are combined ina preselected ratio to facilitate operation of the bioreactor 10. Thiscan be achieve using various flow control features of the invention, andis facilitated in part by incorporation and controlled operation of azone 1 activated sludge return channel 122 and a zone 2 activated sludgereturn channel 124 which receive activated sludge (e.g., via a sludgeextractor line 126 connected to the clarifier) and direct the sludgeinto the zone 1 influent channel 32 or zone 2 recycle channel 110,respectively (see, e.g., FIGS. 2-4, and 8). Flow control within andbetween each of the illustrated feed, flow and drain lines and portsthroughout the appended Figures is readily achieved using flowregulators 50 operatively interconnected with valve or baffle actuators52 and/or flow sensors, all of which are operatively integrated andcontrolled by one or more system control unit(s) 52.

The selected mix ratio per volume of influent of typical municipal wastemay be as high as 3 volumes of clarified effluent and 1 volume of returnactivated sludge to as low as 1 volume of clarified effluent and 1volume of return activated sludge. Approximately 85% of total nitrogenwill be converted to N₂ with 1.75 volumes of either clarified effluentor mixed liquor per volume of influent (see, e.g., Naohiro Taniguchi etal. report on air lift recirculation for nitrification anddenitrification, R&D Division, Japan sewage works agency 1987,incorporated herein by reference.) It should be noted, however, thatsome industrial wastes may require 100 or more recycled volumes pervolume of influent.

With respect to the nitrification process functions of the bioreactor10, this can be further modified or enhanced by selection or adjustmentof the various reactor features and operation parameters describedabove. In addition, the system can readily incorporate, or be coupledwith, additional system features or components to enhance BNR processfunctions. Because the BOD is low in zone 2, growth of BOD-removingorganisms is generally minimized, which allows nitrifying bacteria todominate the biomass. In addition to this advantage, a substantialimprovement in the rate of conversion of ammonium to nitrite and nitratecan also be realized by increasing the concentration of nitrifyingbacteria. Since nitrifiers are attachment organisms, the provision ofattachment sites in a mixed liquor in the form of sponge balls,suspended media, bits of small diameter plastic or rubber (elastomeric)polyethylene tubing, hanging strings of porous fabric in the liquor,etc., can be used quite effectively within the devices and methods ofthe invention (see, e.g., Keith Ganze “Moving Bed Aerobic Treatment”Industrial Waste Water November/December 1998, incorporated herein byreference.) For example, referring to FIG. 4, the BNR processes of thebioreactor can be substantially improved by including suspended media130 that encapsulate or provide substrate for nitrifying bacteria withinthe recycling circulation path of zone 2 (see, also, T Lessel et al“Erfahrungen mit getauchten Festbettreaktorn fur die Nitrifikation”38.Jahrgang, Heft 12/1991, Seite 1652 his 1665, incorporated herein byreference), which modification is facilitated by the novel relativepositioning and interzonal separation between zone 1 and zone 2. Themoving bed media can be prevented from escaping in the effluent, forexample by simple screens. Alternatively, fixed media 132 can be securedwithin in the head tank to increase the biomass of microorganismsadapted for BNR processing. These modifications yield a superior BNRperformance. For example, the combination of a zone 2 regime thatminimizes BOD-removing bacteria along with the increased attached growthbiomass of nitrifying bacteria (e.g. 15-20 g/L equivalent nitrifiers)provides for highly effective BNR processing within the bioreactor ofthe invention. A single sludge extended aeration process typicallycontains 15-20% of nitrifying bacteria (by weight or populationpercentage of sludge mass). However, when attachment media are usedwithin the present invention, the biomass of nitrifiers can be expandedup to greater than 30%, often up to 60-70%, as much as 75-85% or more ofnitrifiers in the system population. This relates to the relativeexhaustion of BOD in this process stage and zone of the system, as wellas to the effective use of fixed or circulating attachment media withinzone 2. These novel features and characteristics distinguish themodified single sludge system of the present invention from other singlesludge processes.

Within additional aspects of the invention, a novel nitrificationprocess is provided which relies substantially or entirely upon residualdissolved oxygen originating near the bottom of zone 1 as the source ofoxygen to drive the process. Yet another important benefit anddistinction that arises by using the unspent gases from zone 1 in thisfashion is the high level of CO₂ available, which is also required bynitrifying bacteria as a source of inorganic carbon. In othernitrification systems, the primary inorganic carbon source depends onalkalinity of the wastewater and is typically determined by the presenceof CaCO₃. The bioreactor process systems of the invention are thereforemore compact and require less energy than current, extended aerationsystems. Bioreactors constructed and operated according to the inventionalso produce a better quality biomass (including class A biosolids ifdesired) that is easier to separate from the mother liquor.

To further enhance the functions and operation of the bioreactor 10 ofthe invention, various coupled or integrated features can beincorporated with the bioreactor for enhanced processing of waste water.As illustrated in FIG. 2, the bioreactor according to the invention foruse in waste water treatment may incorporate a conventional, stand-alonesedimentation clarifier 120. The bioreactor is further optionallyfluidly connected with an aerated polishing biofilter 133 and/or anultra violet light disinfection chamber 134 and/or back wash tank. Incertain embodiments, line 136 returns backwash to the influent.

Alternatively, FIGS. 3 and 8 (schematically and by partial sectionalperspective views, respectively) illustrate an additional embodiment ofthe bioreactor 10 according to the invention—featuring an integratedcircular sedimentation clarifier 120′ surrounding a circular zone 2 headtank 15 which in turn surrounds a circular zone 1 head tank 16 (allthree tanks being concentric in this vertical reactor). In theseembodiments, settled activated sludge is returned by gravity to eitherzone 1 or zone 2.

Alternate embodiments of the bioreactor 10 illustrated in FIG. 4 featuremoving bed media 130 circulating in zone 2 and, additionally oralternatively, fixed media 132 suspended in the head tank 15 of zone 2.Another embodiment, as illustrated in FIG. 5, incorporates a pressurizedhead tank 135, and an optional off gas collector 136 (see, e.g., U.S.Pat. No. 4,272,379 to Pollock, incorporated herein by reference), forexample with off gas driving an air lift influent pump 137 required toovercome the head tank pressure, as well as an optional membranefiltration cartridge 138 (see, e.g., George Heiner et al, “MembraneBioreactors” Pollution Engineering December 1999, incorporated herein byreference) operating under pressure to separate biomass from liquid anda clean water, ultraviolet (UV) disinfecting chamber 139 also serving asback wash storage for membrane backwashing. Still other embodiments, asshown in FIG. 6, feature an integrated clarifier 120′ fluidly connectedto an aerated polishing biofilter 133 and an ultra violet lightdisinfection chamber 134 and filter back wash tank.

Typically, for long vertical shaft bio-reactors, the optimum biologicalair supply rate required for bio-oxidation process creates excessive“voidage” at the top of the reactor, comparable in the present case tothe superior upflow channels exemplified by the zone 1 upflow channel 40and zone 2 upflow channel 82. Excessive voidage produces undesirableslugging (water hammer), which can cause reactor damage attributed tovibration. The occurrence of slugging air voidage also signifies pooroxygen transfer characteristics within the circulating fluids. Theinvention addresses these problems in a number of ways, including byproviding novel means for regulating circulation velocities andmodulating gas content in selected parts or channels of the reactor.

Since oxygen transfer rate and oxygen utilization rates are relativelyslower than upward hydraulic velocities in the reactor 10, increasingvelocity only reduces the operating efficiency of the reactor. Increasedflow decreases bubble contact time and slows oxygen transfer, thus moreaeration is required to optimize the process. Similarly, reducingaeration reduces reactor capacity. One proposed method for resolving airvoidage and related problems is presented in U.S. patent applicationSer. No. 09/570,162, filed May 11, 2000 (incorporated herein byreference) describing the “VerTreat II” bioreactor. In this disclosure,flow velocity is beneficially reduced by incorporation of an orificeplate in the lower section of the riser channel. However, this solutiondoes not substantially resolve the problem of slugging, and the orificeplate creates additional problems including risk of fouling and flowaberrations particularly in small municipal plants.

The bioreactor 10 of the present invention resolves these problems inpart by incorporating a novel relative configuration of zone 1 and zone2. Unlike the previously described “VerTreat I” bioreactor (see, e.g.,U.S. Pat. No. 5,650,070, issued Jul. 22, 1997, incorporated herein byreference), where zone 2 is below zone 1 and therefore no voidagecontrol in zone 2 is possible, the present invention can control flowand gas content in each zone, independently. Conventional prior art“Deep Shaft” reactors start slugging at a upflow velocity of about 2feet per second. The above-noted VerTreat II reactors with orificeplates can operate down to about one and a quarter feet per second.Within the present bioreactor, this value can be dampened to as littleas one quarter to one half feet per second in the lower part of theriser channel. At lower riser velocities, some heavier solid particleswill settle into the sump 67. These solids are conveniently extracted,along with surplus biomass (e.g., circulating within the shear header 70and surrounding mix zone 18) when desired, by purging of thedual-purpose aeration/solids extraction line 66.

The invention provides substantially more efficient new features andmethods for slowing velocity over prior art methods, which includes theability to dilute the air lift stream in one or more superior upflowchannel(s) of the reactor with bubble free fluid, as described above.The advantage of these features and methods over the VerTreat IItechnology includes the elimination of potential plugging of the orificeplate in the lower and inaccessible section of the riser channel, whichis particularly problematic in smaller diameter reactors.

In long vertical air lift reactors such as the bioreactor 10 of theinvention, where fluid/gas mixtures are caused to circulate in verticalchannels, the volume of gas in a defined volume of liquid changes withthe pressure (gas laws). Consequently at the bottom of the reactor, thevolume of gas in liquid (voidage) is small, whereas at the top of thereactor the same expanded gas volume to liquid volume ratio is manytimes larger. Since 34 feet of water is equivalent to about oneatmosphere of pressure, it can be readily calculated that 1 cubic footof air on the surface (1 scf) becomes 0.5 cubic feet at 34 feet depthand 0.33 cubic feet at 68 feet and 0.25 cu. ft. at 102 feet. Thereforeintegrating the area under the volume vs. depth curve shows 78% of thegas volume voidage occurs in the top 102 feet of the reactor.

Many studies on air-lift pumps and other bubble/water columns show thatslugging in water occurs at 11-14% voidage. Slugging is undesirablebecause the bubbles coalesce into large air pockets which set upvibrations in the reactor, and most importantly, large bubbles have verypoor oxygen transfer characteristics. Proposed controls of voidage toameliorate these effects have been attempted in at least two differentways. One proposed control is to increase the reactor cross sectionsufficiently to allow disengaging the gas from the gas/liquid mixture.Alternatively, efforts have been undertaken to maintain residualpressure on the gas/liquid mixture at the top of the reactor. Each ofthese proposed controls have attendant drawbacks making them undesirablefor use within the bioreactor of the present invention. For example,head tank designs of some air-lift reactors are provided where liquiddepths of ½ atmosphere (17 feet) are used. This reduces the maximumvoidage by 17%, but head tank depths much deeper than 17 feet aredifficult to construct. In addition, tall head tanks above groundrequire pumping influent against a significant hydraulic head, wastingsubstantial energy.

The invention provides novel features and method for controlling voidageand ameliorating the adverse effects of slugging. Briefly, thesefeatures and methods reduce the quantity of bubbles per unit of fluid inone or more selected channels or chambers of the reactor 10, either byadding more fluid or reducing the gas. In more detailed aspects, liquidflow in one or more superior upflow channels of the reactor is increasedby recycling liquor from an upper segment (e.g., 60-90′) of the reactor,through a degas step, and back down to a lower, recycling influx pointnear the bottom of the upper segment (e.g., 60-90 feet below thesurface). It is generally considered that total gas flow (air flow) isdetermined by biological optimization requirements, however this totalgas flow can also be proportioned into selected, superior upflowchannels in the upper part of the reactor using novel flow controlmechanisms described herein.

Because approximately 75-80% of the voidage occurs in the top 60-90 ft.of the reactor, the recycle channels (exemplified by the influentchannel 32 which optionally nested receives zone 1 recycle input fromzone 1 recycle port 140, and the zone 2 recycle channel 110), are onlyabout 25-35% of the total depth of a typical bioreactor and occupy onlya small fraction of the reactor cross section area and volume. Inpractice, zone 1 and zone 2 of the reactor comprise approximately equalfluid volume, but in the case of BNR removal zone 2 is expanded involume for nitrification by increasing the diameter of the zone 2 headtank 15. The voidage in the zone 2 recycle channel can be readilycontrolled under a wide range of operating conditions by designing forsufficient, adjustable recycle flow of degassed liquor from the zone 2head tank 15 as regulated by the zone 2 recycle regulator 112. Thebubble volume in the zone 1 upflow channel 40 can therefore be dilutedby degassed liquor to the extent limited by the acceptable range ofminimum and maximum values for influent flow, which is somewhat limited.To resolve this limitation, a regulated amount of liquor may be divertedthrough the zone 1 recycle port by adjustment of the zone 1 recycle flowregulator 50 (effectuated by operation of the system control unit 51).Controlling flow from the head tank in this coordinated manner isnecessary to maintain gravity feed of the effluent.

The instant invention therefore provides a number of separate andoptionally cooperative mechanisms and methods to alleviate the problemsof slugging at low bioreactor 10 flow velocities. In another aspect,this problem is alleviated by providing a choice of adjustable diverteror baffle devices, exemplified by the fixed or adjustable divertermechanism 84. The configuration (including size, shape, location andorientation) of this exemplary diverter plate can be fixed at the timeof construction and installation of the reactor. Alternatively, theseand other flow diverter parameters can be selectably altered, forexample by employing a manual or motorized diverter plate adjustmentmechanism optionally integrated for functional control (e.g., to controlpositional and orientation parameters) by the system controller 51.Operation of the flow diverter serves to direct a greater or lesserfraction of air bubbles entrained in the upflow from the primary reactorchannel 80 into one or more selected superior channels, for example todivert a greater fraction of the fluid-bubble mixture toward the zone 2upflow channel 82, allowing a lesser to pass upward into the zone 1upflow channel 40.

Once the desired fraction of bubbles have been thus diverted into thezone 2 upflow channel 82, the voidage in this channel can be easilycorrected by changing the amount of zone 2 recycle flow throughadjustment of the zone 2 recycle flow regulator 112. The circulatoryloop (following arrows between zone 2 upflow channel 82, across zone 2degas plate 150, through zone 2 recycle regulator 112, down zone 2recycle channel 110, and through zone 2 shielded recirculation port152), together with a surface basin or zone 2 head tank 15 at the top,comprise zone 2 and represent the polishing process and optionalnitrification features of the bioreacter which are driven by waste gasfrom zone 1. The configuration of the diverter which segregates flowinto the superior upflow channels prevents liquor transfer from zone 2into zone 1, since both liquid and air flow in the zone 2 upflow channel82 is unidirectionally upward. In this regard, as noted above, zone 2circulation characteristics are ideal for the application of fixed media132 (FIG. 4) and, alternatively or cooperatively, membrane separationcomponents (FIG. 5). Moving bed media 130 (FIG. 4) can also be used,since zone 2 circulates completely separately from zone 1, to enhancenitrification within alternative process modes of the reactor.

Hydraulically, any influent flow into zone 1 of the bioreactor 10 (andany required external recycle streams from the clarifier 120 or zone 2head tank 15) that enter zone 1 must leave zone 1 by entering the bottomof zone 2. Since zone 1 is a closed loop, namely zone 1 upflow channel40, zone 1 head tank 16, downcomer 12 and primary reactor channel 80,the number of recycles in this loop and the liquid velocity dependsdirectly on the volume of air bubbles diverted by diverter plate 84 intozone 1 upflow channel 40. For example, in a typical municipal effluentof 200 mg/L of BOD, the number of internal recycles is approximately theBOD in mg/L divided by the O₂ potential in the reactor, divided by theoxygen transfer efficiency. In a 250 ft. deep reactor, oxygen isinjected at about 7.3 atmospheres of pressure. Solubility of O₂ in waterat 1 atmosphere and 20° C. is about 8 mg/L. This means the dissolvedoxygen potential at 7.3 atmospheres is 7.3×8=59 mg/L or about 40 mg/L atan oxygen transfer efficiency of 70%. Therefore, the minimum number ofrecycles is 200 divided by 59×0.70=about 5. In practice 6 or 7 recyclesmight be used as a safety factor. A hydraulic loss calculation willdetermine the fraction of air required for 6 or 7 internal recycles;e.g., 30% of the air that is applied at the bottom of zone 1. As theorganic load to the plant increases or decreases, the air rate isadjusted accordingly, causing the number of internal recycles toincrease or decrease to satisfy the BOD requirement. However, 30% of theair applied remains consistent, constant as determined by diverter plate84 placement. Field trimming is achieved, for example, by adjustingregulator valve 50, which changes recycle flow within the air liftsection at zone 1 upflow channel 40, thus reducing or increasing its airlift capability.

Similarly, any flow from zone 1 that enters zone 2 must leave aseffluent from zone 2. Since the lower portion of zone 2 comprisingupflow channel 82 and adjacent downflow channel 10 typically has nointernal recycle connection with zone 1, any air diverted from zone 1into zone 2 will simply cause circulation in the superior channel(s) ofzone 2 with no change in the circulation rate of zone 1 (change in airrate in zone 1 does, however, affect the circulation rate in zone 2, butnot vice versa).

Therefore, within certain aspects of the invention, diverting forexample 70% of the air originating at the bottom of zone 1 into zone 2only affects the circulation in zone 2 which can be easily controlled bythe zone 2 recycle regulator 112. Hydraulically, influent flow into zone1 upflow into zone 2 and effluent from zone 2 within the reactor 10 areequal in quantity, i.e., influent flow entering the reactor in zone 1exits through zone 2. With reference to prior art vertical bioreactorstreating municipal waste, the internal recycle flow is about ten totwelve times the influent flow, or effluent flow. The present process,which features novel air lift controls as described above, can reducethis flow by about a 2-3 fold reduction, often a 5-6 fold or evengreater reduction.

By adjusting the configuration of the diverter (generally referring toany diverter device for segregating flow from the primary reactorchannel 80 into a plurality of superior upflow channels), the selectedbubble fraction only (not typically the same as the liquid flowfraction) in the primary reactor channel can be segregated among anydesired number of channels (typically 2, 4 or 6, depending on reactorsize and purpose) in any ratio selected to achieve optimum operation ofzone 1 and zone 2 (note that each superior channel shown in FIG. 8 has acompanion channel opposite it, which is a typical layout for largerreactors using two or more clarifiers. Smaller reactors have only 4channels and a center downcomer, as illustrated in FIG. 7). For example,typical flow values in the zone 1 upflow channel 40 may be selected tobe 6-8 times (alternatively, 2-3 times with BNR) the flow entering zone2 at the top of zone 1 at the level of the diverter plate 84(immediately below the zone 2 upflow channel 82), but only require20-30% the amount of air to produce a non slugging air lift effect.Alternatively, when not using BNR, the flow into the zone 2 upflowchannel may be selected to be about one sixth the flow in the zone 1upflow channel, but conversely receive about 75-85% of the air. Air flowsettings into the zone 2 upflow channel can thus be set over a broadrange of flow settings, for example 10-15%, 20-30%, 30-50%, 50-75%,75-90% or greater.

After diluting the zone 2 upflow, for example using 8 to 10 times therecycle flow from the zone 2 head tank 15 via the zone 2 recycleregulator 112, the air lift effect in the zone 2 upflow channel can bereadily controlled. This control depends on the novel mechanisms andmethods set forth above for segregating flow in an aerated and flowingvertical column, providing for selectable channeling of flow indifferent proportions into two or more other superior vertical columns,while the air bubbles may be split in a completely different ratio amongthese vertical columns. This novel ability to control air lift allows abetter biological match between oxygen supply (dependent on the timeavailable at pressure to dissolve oxygen, which is in turn a function offlow velocity) and oxygen utilization which is a function of respirationrate, (dependent on dissolved oxygen—not primarily upon the amount ofbubbles present).

Within yet another aspect of the invention, novel features and methodsare provided for addressing the challenges involved in the disposal ofby-product sludge and/or surplus bio-solids from the bioreactor 10treatment processes. Recognizing the nutrient value of these biosolids,the EPA in the US adopted 40 CFR 503 in 1993, which proscribes variousprocess criteria to achieve class A bio-solids for unrestricted use as asoil supplement. Whenever possible, beneficial reuse of bio-solids isencouraged. One set of criteria for Class A bio-solids requires aminimum volatile solids reduction, as well as a Time-Temperaturerelationship, for example a 38% volatile Solids reduction and a 60° C.temperature for 5 hours qualifies as a Class A product. FIG. 12

Within a modified embodiment of the invention, referring to FIG. 7, thebioreactor 10 is designed to function alternatively as a waste sludgedigester and to meet the minimum volatile solids reduction andTime-Temperature relationship criteria for Class A biosolids production.In this regard, the reactor is specially designed and operated with aunique flow and zonal separation regime that provides for production ofClass A biosolids in as little as 5-6 days, often in 3-4 days or less,using thermophilic bacteria operating at 58-65° C. but typically 58°-62°C. and often 60° C. The 38% volatile solids reduction is a measure ofstability of the biomass or vector attraction reduction (VAR), while theelevated temperatures pasteurize the product to control E-coli andvirtually eliminate salmonellae. Consuming 38% of the volatile matterminimizes odor potential and provides enough food energy forThermophilic bacteria to raise the temperature of the reactor to over60° C., without applying exogenous heat.

Published data demonstrate two areas of concern for existing verticalshaft bioreactors that seek to produce class A biosolids (see, e.g.,Report on VerTad operations King County Wash., project 30900 May 20001,incorporated herein by reference.) First, small vertical bioreactors(e.g., “VerTad reactors”, as described for example in U.S. patentapplication Ser. No. 09/570,162, filed May 11, 2000 (incorporated hereinby reference), feature a relative disposition of zone 2 (polishing zone)below zone 1. These reactors have a comparatively large surface area tovolume ratio, and excessive heat is lost to the surrounding geology.Small reactors therefore require supplemental heat to support class Abiosolids production, which is available at additional cost byrecapturing the waste heat from the compressor or from the hot effluentstream.

A second area of concern for previous vertical bioreactors directed tohigh quality biosolids production is that there is insufficient liquidto liquid separation between zones 1 and 2. Published data of tracerstudies in VerTad reactors show that the zone 2 (polishing zone) behavesas a plug flow reactor, with a critical feature of localizedback-mixing. Over a period of about 8 hours, zone 2 begins to mix withzone 1 and the whole system (zone 1 and zone 2) is mixed in 16-20 hrs.Accordingly, some solid particles, potentially containing salmonellae orother prohibited contaminants, can settle from zone 1 into zone 2without being exposed to the required retention time at pasteurizingtemperature to meet class A biosolids requirements.

The improved bioreactor/digester 10′ of the present invention isconfigured in a distinct manner with zone 1 surrounding zone 2 (FIG. 7),such that for any given volume of reactor the surface to volume ratio issmaller than in previously described reactors directed to qualitybiosolids production, whereby the heat lost to the surrounding geologyis much less. The improved bioreactor/digester provides enhanced liquidto liquid separation at a transfer point between zone 1 and zone 2. Thetransfer point is delineated by an air lock mechanism 172 (e.g., adiaphragm-less air operated valve) typically including an air lockbaffle 170 as depicted in FIG. 7. The baffle extends upward into an airpocket formed by the introduction of clean, pressurized air from adedicated air line 62 with air delivery port 64 or aeration/solidsextraction line with corresponding port 68 located near sump 67. Zone 1is aerated through port 69

Within this aspect of the invention, it is considered critical that whenthe apparatus is being used as an aerobic thermophilic sludge digester,bubbles from zone 1 must not enter zone 2 because of the risk ofre-inoculating the pasteurized product in zone 2. To prevent this fromoccurring, pressure in the air lock is maintained by fresh cleancompressed air, and there is no liquid flow or contact between zone 1and zone 2 or transmission of contaminated air from zone 1 to zone 2.The air lock is designed to prevent inter-zonal mixing of liquid betweenbatches, ensuring that zone 1 does not re-inoculate the pasteurizedbiomass in zone 2 with pathogenic bacteria during batch processing. Asan example, one batch of sludge may be processed every 5-8 hours, thusensuring that the critical time temperature of 60° C. for five hours isalways met within each batch.

In operation of this embodiment of the invention, waste biomass is fedcontinuously or intermittently into the reactor/digester 10′, e.g., intothe zone 1 head tank 16′. As the head tank level in zone 1 rises abovethat of the zone 2 head tank 15′ level, a pressure differential developsacross the center baffle 170 in the air lock. Eventually the zone 1liquid level in the air lock exceeds the baffle height and fluidtransfers from zone 1 to zone 2. Line 64 air supply is placed slightlybelow the liquid level of zone 2 within the airlock, whereby at thefirst onset of flow between zone 1 and zone 2, the bubbles are sweptaway into zone 2 and the air lock collapses. Flow stops when the headtank levels are again equal and the airlock re-establishes itself. Abatch can also be initiated by draining the zone 2 head tank 15′. FIG. 7shows zone 2 head tank being drained and the air lock approaching batchtransfer. The size of the batch is the change in head tank levelmultiplied by the surface area of the tank. Therefore the baffle 170need only penetrate into the air lock 172 by a foot or two because 1-2ft. of liquid level change in the head tank would typically represent afull batch. The additional hydraulic considerations in this aspect ofthe invention are similar to those set forth for the precedingembodiments.

When the bioreactor 10′ functions as a waste sludge digester (see, e.g.,FIG. 7), thickened waste sludge, generally 4-5% solids by weight, is fedinto the reactor, for example through influent conduit 30. The feed canbe continuous, or batch wise, depending on the operation of the wastewater treatment system generating the sludge. The raw sludge typicallydescends into the reactor through influent channel 32, and is met with azone 1 upflow stream 40′ containing an elevated percentage of airbubbles (e.g., 10-15%). The combined streams are less dense than theinfluent stream 32′ or flow in the downcomer channel 12′ and as aresult, downward circulation is induced in the downcomer channel and inthe influent channel. In this way influent is drawn into the reactor andcirculation and aeration occur in zone 1. In FIG. 7, it is important torealize that the head tank circulation from zone 1 upflow channel 40′ tochannel downcomer channel 12 is behind the zone 2 head tank 15′ asindicated by the broken arrows.

In addition to zone 1 and zone 2 being hydraulically separated by adiaphragm-less air valve (air lock 172), the lower portion of each zonefunctions as a pseudo plug flow zone while the top portion of each zoneis circulated in the superior channels and is well mixed. As a resulteach of zone 1 and 2 is further divided into two additional smallerzones to double guard against reinocculation of the finished productwith the raw influent. When the present invention is used as a sludgedigester, baffle 86 extends to about 70-90% of the reactor depth andbaffle 84 completely seals off the bottom of zone 2 from zone 1. Forcertainty that no cross contamination can occur, zone 2 may be furthersealed with second outer wall 197 in close proximity to the outer casing196 as shown in FIG. 10 and FIG. 11. The air locks 170 are shownpenetrating the septa wall between zone1 and zone 2 at a location abovebaffel 84, but below ports 34 and 152. Zone 1 has an aerated volumebelow zone 2 of at least one batch volume and preferably two.

The reactor/digester 10′ of FIG. 7 is thus very similar in its operationto the waste water treatment reactor illustrated in FIG. 1, but differsin four principal aspects:

-   -   1. The zone 1 surrounds zone 2;    -   2. Zone 2 extends downward about 70-90% of the depth of the        reactor within zone 1;    -   3. Each zone has its own aeration means;    -   4. There is liquid to liquid separation between zone 1 and zone        2 through use of the airlock 172.    -   5. Each of zone one and zone two is further divided into an        upper circulating zone and a lower pseudo plug flow zone.

Once sludge enters the reactor/digester 10′ it has a mean residence timeof approximately 2 to 3 days in zone 1, and 2 to 3 days in zone 2. TheEPA criteria for the production of class A bio-solids dictates the timebetween batches, which varies with temperature—as an example the minimumresidence time for a batch at 60° C. is 5 hours, or about 4.8 batchesper day. Therefore, zone 1 and zone 2 theoretically contain between 9.6and 14.4 batches each. In practice, however, each batch would be about 8hours, and therefore zone 1 and zone 2 would contain between 6 to 9batches each. The overall residence time is determined by thebiodegradability of the sludge. For class A bio-solids, the process mustachieve a minimum of 38% volatile solids reduction which typically takes3.5-5 days. The batching time is determined by the temperature (see,e.g., FIG. 12). The preferred operating temperatures of 58° C.-62° C.require approximately 8-4 hours.

As noted above, the air line 62 can be operated to maintain the airpressure in the air lock 172 of the reactor/digester 10′ to controlbatching. Stopping the air flow in line 62 will also trigger a batchdischarge after the appropriate processing time has elapsed. A batch canalso be triggered by lowering the liquid level in the zone 2 head tank15′. Once the batch in zone 2 is discharged, the head tank level in zone1 is automatically lowered an equal amount by the action of theautomatic batching valve located between the bottoms of zone 1 and 2,and the cycle repeats. When a batch is processed through the reactor, itis reduced in solids content from approximately 4-5% down to about 2-3%.This product (class A biosolids) may then be de-watered.

Published research by The University of Washington (Guild et al.,Proceedings of WEF Conference, Atlanta Ga., 2001, incorporated herein byreference) indicates that when thermophic aerobic digested sludge from avertical shaft reactor having certain features in common with thereactor of the present invention was fed to a mesophilic anaerobicdigester, the retention time in the anaerobic digester was reduced, theoverall volatile solids reduction was better, the dewaterability wasbetter and required less polymer. The thermophilic aerobic digester isoperated with a about a 2 day retention time and can generate enoughheat to comply with Class A biosolids.

It is well documented that during the aerobic thermophilic digestion ofbiomass, there is minimal nitrification of ammonia at temperatures above42° C. It is also well documented that in anaerobic digestion of biomass(where there is no air stripping), ammonia and carbon dioxide react toform ammonium bicarbonate. In a vertical aerobic thermophilic digester,it is reasonable to believe that ammonium bicarbonate also forms, due tolarge amounts of both ammonia and carbon dioxide remaining in solutiondue to pressure.

The selection of operating temperatures is very important in long,vertical thermophilic aerobic digesters because ammonium bicarbonatedecomposes at about 60° C. Ammonium bicarbonate is very important in theefficiency of the solids liquid separation (dewatering) step of theprocess. For instance, when operating a deep vertical thermophilicaerobic digester at 55° C. to 58° C., the digested sludge samples werevery granular before drying the sample but not after drying at about104° C. On one occasion when the head tank was opened without coolingthe reactor (for emergency repair of a float switch), the insidesurface, particularly the uninsulated access cover, was coated with tinywhite angular crystals much like white sugar or salt. These crystalssubsequently disappeared and were not found again at the higheroperating temperatures. Another observation that is common, is that whena batch of product is transferred into the soak zone at about 58° C.(where there is negligible biological activity), the temperatureincreases and holds constant for about 2 hours, then cools at thecool-down rate of the reactor when operating on hot water. The heat ofcrystallization of 10,000 mg/L of ammonium bicarbonate would account forthe apparent heat generated in the soak zone. Empirically, theseobservations would suggest the formation of ammonium bicarbonatecrystals below 60° C. This is contradicted by the fact that ammoniumbicarbonate is very soluble in water, but less so in the presence ofhigh levels of other dissolved solids, and perhaps the surface chemistryof the microbiology facilitate the crystallization process. Forinstance, Struvite (magnesium ammonium phosphate) is readily formed inanerobic digesters of plants using biological phosphorus removal but notin plants using chemical phosphorus removal. Controlling the reactortemperature to below 60° C. may allow ammonium bicarbonate crystals toform which would easily float separate with the sludge.

Table 1 compares the performance of floatation, nutrient fractionation,and dewaterability of thermophical aerobic digested sludge that wastaken from a deep vertical thermophilic aerobic digester similar to thepresent invention. It is known that thermophically digested sludge willdewater better than anaerobically digested biosolids however at muchhigher polymer dose. Previous studies investigated the cause of the highpolymer requirement and found that monovalent ions such as sodium,potassium, and particularly ammonium ions can interfere with thecharge-bridging mechanisms in the floc. In conventional thermophilicaerobic digesters the nitrification of ammonia is inhibited over 42° C.and therefore the ammonia produced is in largely in solution, asevidenced by typically high pH. The carbon dioxide produced issubstantially stripped out by the large air flows required in thesedigesters and less carbon dioxide remains in solution to form ammoniumbicarbonate. Since the air bubble contact is in the order of seconds,and the rate of solution of ammonia is much faster than that of carbondioxide, the environment does not favor the formation of ammoniumbicarbonate.

TABLE 1 Nutrient Fractionation CF is Concentration Factor Stream TS % CFTN mg/L CF NH₃ mg/L CF ORG-N mg/L CF TP mg/L CF Cake % Poly #/T pH7.8-8.0 T ° C. Under 60 (59-60.5) 4.80% Digested Vertad Sludge Digested4.8 4780 1163 3095 970 2.2 2.4 1.6 3.1 2.8 Float 10.7 11347 1860 94872750 7.1 1.2 50 24 0 Recycle Clear 1589 1570 19 115 pH 8.5-8.8 T ° C.Over 60 (61.5-63.5) 3.80% Digested Vertad Sludge Digested 3.8 1851 8021049 548 26-30 50-70 1.5 1.7 1.2 2.1 1.3 Float 5.6 3185 948 2238 70431-34 14 3.4 1.8 9.9 1.6 Recycle Turbid 927 702 225 442

It is believed that below 60° C. ammonium bicarbonate forms in a deepvertical bioreactor due to the high level of carbon dioxide and ammoniain contact and under pressure for long periods of time. Above 60° C.ammonium bicarbonate decomposes and the carbon dioxide and ammonia arestripped out with the air stream, very similarly to the conventionalthermophilic aerobic processes. When the final product, processed below60° C., is acidified with sulfuric acid, alum, or ferrous sulphate, etc,ammonium sulfate is formed and CO₂ is released, thus floating thesludge. Unexpectedly, the floated product dewaters exceptionally well.In recent reports by Murthy et al. (Mesophilic Aeration of Auto ThermalThermophilic Aerobically Digested Biosolids to Improve Plant Operations,Water Environment Research 72, 476, 2000; Aerobic Thermophilic Digestionin A Deep Vertical Reactor, Project 30900, Prepared for King CountyDepartment of Natural Resources, Mar. 28, 2001, each incorporated hereinby reference) the concentration of biopolymer (proteins andpolysaccharides) in thermophilically aerobic digestion could beminimized by limiting the residence time of the thermophilic digestion.The present invention has ⅓ to ½ the residence times of conventionalthermophilic aerobic digesters. The presence of biopolymer andmonovalent ions, particularly ammonia, in solution correlates well to anincrease of polymer consumption. The formation of ammonium bicarbonatewould significantly reduce ammonium ions.

Lowering the pH with acid to about 5.0, causes the biosolids to float toabout 10-12% concentration. Lowering the pH to 4.5-4.0 and lower yieldsa faster float separation but may require adjustment, e.g., to pH5.5-6.0, which is the pH range of the sludge before digestion. Digestionbelow 60° C. controls the reactor pH to 7.8-8.0 while digestion over 60°C. results in an operating pH of 8.6-8.8, reflecting the effect of morefree ammonia due to the decomposition of the ammonia bicarbonate.Flotation separating is better below 60° C. than above 60° C., in allcategories, where the less acid used yields a thicker float blanket andbetter nutrient fractionation. These biosolids can be furthercentrifuged to 30-35% solids concentration using a low polymer dose ofabout 15 pounds polymer per ton dry weight biomass. The acidificationprocess may cause some cell lysis, which will also help dewater thesludge.

These results are substantially better than conventional thermophilicaerobic digestion processes which require 30-50 pounds polymer per tondry weight biosolids and centrifuge to only 20-25% solids. Acidifyingthe conventional thermophilic aerobic digester product does not floatseparate the solids, presumably due to the lack of ammonium bicarbonate.

Examination of the data in Table 1 shows the profound effect onflotation, dewatering, and nutrient fractionation, between operating thereactor under 60° C. and over 60° C. Operation under 60° C. generatesless free ammonia and more ammonium bicarbonate, therefore the pH islower and there is less ammonia in the off-gas. In order to get a commonbase for a comparison between the two sets of data, a concentrationfactor is calculated. The concentration factor [CF] is the ratio of thefinal concentration to the starting concentration.

Looking at the “under 60° C.” set of data the float solids were 2.2times more concentrated compared to the digested sludge solids; thetotal nitrogen in the float was 2.4 times as concentrated; the ammoniain the float was 1.6 times as concentrated; the organic nitrogen was 3.1times as concentrated; and the total phosphorus was 2.8 times asconcentrated. Except for ammonia the nutrient concentration factorranged from 2.4 to 3.1 when the solids concentration factor was 2.2.

Looking at the “over 60° C.” set of data the float solids were 1.5 timesmore concentrated compared to the digested sludge solids; the totalnitrogen in the float was 1.7 times as concentrated; the ammonia in thefloat was 1.2 times as concentrated; the organic nitrogen was 2.1 timesas concentrated; and the total phosphorus was 1.3 times as concentrated.The nutrient concentration factor, including ammonia, ranged from 1.2 to2.1 when the solids concentration factor was 1.5.

These data strongly suggest that the nutrient fractionates into thesludge solids in nearly the same ratio as the solids concentrationfactor (except for ammonia under 60° C. which is explained later). It isexpected that the same fractionation will also occur during dewateringof the floated solids.

However, looking at the float solids concentration factor compared tothe subnatent or recycle stream, a completely different and surprisingdiscovery emerges.

The “under 60° C.” set of data shows the total nitrogen in the float was7.1 times as concentrated as in the recycle; the ammonia in the floatwas 1.2 times as concentrated; the organic nitrogen was 500 times asconcentrated; and the total phosphorus was 24 times as concentrated.Except for ammonia all the nutrients shifted dramatically from the clearrecycle into the sludge solids. In other words, except for ammonia, theother nutrients are substantially removed from the recycle streams thusbenefiting the operation of the treatment plant and improving thenutrient value of the bio-solids

The “over 60° C.” set of data shows the total nitrogen in the float was3.4 times as concentrated than in the recycle; the ammonia in the floatwas 1.8 times as concentrated; the organic nitrogen was 10 times asconcentrated; and the total phosphorus was 1.6 times as concentrated.Except for ammonia and phosphorus, the nutrient shifted significantly,but less dramatically from the turbid recycle into the solids.

A possible explanation of the minimal shift of ammonia into the solidsis that the acidification of ammonium bicarbonate results in ammoniumsulphate which is very stable but very soluble. The shift in the organicnitrogen to the sludge solids is likely because organic nitrogen ispresent in the particulate matter of digested sludge and would likelyfloat separate. The ammonium bicarbonate crystals, if any remain afteracidification, might also float separate as particulate matter. Theshift in phosphorus to the sludge solids by acidification of the sludgecan be explained by the formation of insoluble precipitates in thepresence of a high concentration of metals occurring naturally in thesludge. This effect is not so pronounced over 60° C., probably becausethe float separation was poor and the tiny particles formed in theprecipitate are difficult to float.

In constructing and installing the improved vertical shaft bioreactor 10of the invention, twin bioreactors (to satisfy EPA redundancyrequirements) will often be placed in cased and grouted steel shaftsapproximately 36 inches in diameter and 250 feet deep. The exemplaryscope and reactor design described here for illustration purposes issuited for a community of about 5000 people requiring a tertiarytreatment plant with biological nutrient removal would proceed asfollows. Also described here for illustration purposes is a novel,modular bioreactor assembly design, while it will be understood that theuse of a modular assembly method is not necessary to practice theinvention.

The inner head tank for this exemplary installation is about 8 feet indiameter and approximately 12 feet high. The shop fabricated reactorinternals include 6 flanged tube bundles each about 40-ft. long. Thebottom 40-ft. length (first length) is made up of the aerationdistributor 60, the shear header 70, the airlines 62 and 66, attached toa short length of downcomer 12. The second, third and fourth tubebundles, include 40 ft., modular sections 190 typically including acentral downcomer conduit 22 with airlines 62 and 66 attached (see,e.g., FIGS. 9-11). These sections are joined, e.g., bolted, togethersequentially at modular section joints 192 to the preceding section asthe sections are sequentially lowered into the shaft. The top twosections, 5 and 6, comprise the downcomer air lines and superiorchannels formed as a unit by using the central downcomer 22 and radialchannel partitions 194. After installation, the radial partitions willassume a light press fit in the reactor shell (e.g., against an innerwall 196 of the riser conduit 24.

To facilitate modular construction of the bioreactor 10, the superiorchannel-forming radial partitions 194 are relaxed from the inner wall196 of the reactor during insertion by expanding the diameter of thecentral (e.g., downcomer 22) conduit in a direction generallyperpendicular to the radial partition (see, e.g., FIG. 11). To expandthe downcomer conduit in this manner, FIG. 9 depicts a novel conduitexpansion device 198, which is provided, for example, in the form of aspreader sized and dimensioned for insertion within the downcomerconduit. The spreader typically has paired, opposed and reciprocatingspreader parts 200, 202, which can be manually, reciprocatinglyrepositioned between relaxed and expanded configurations (e.g., byremotely turning a threaded expansion driver 204 that engages each ofthe reciprocating spreader parts and causes them to spread in thedirection of the outwardly directed arrows in FIG. 9, or tocooperatively relax in the opposite direction). Thus, FIG. 10 provides adiagrammatic end view of the reactor internal section showing thedowncomer and radial baffles. The expansion tool 198 in the center ofthe downcomer conduit 22 is shown in its relaxed position. Accordingly,in this Figure the downcomer is also in its relaxed position. FIG. 11provides a diagrammatic end view of the reactor internal section showingthe downcomer forced out of round by the expansion tool in its expandedconfiguration, wherein the radial baffles 194 connected to the downcomerare forcibly retracted away from the inner casing wall 196 to allowinsertion of the reactor section 190 therein. When the invention is usedas a digester, a sealed zone 2 can be provided by adding a second outerwall 197 on half the assembly. Because this second wall is applied toonly half the circumference, it does not prevent the spreaders fromdeforming the center tube thus relaxing the wall pressure of the septapartitions during installation.

After assembly to this stage is complete, the zone 1 head tank 16 isbolted to the top of the last section. The zone 2 head tank 15 isfield-erected from pre-fabricated sections. The modular reactor tubebundles can be delivered to a site for installation by a single truck,and the head tanks by a second truck. The clarifier 120 shell can becast in place using concrete or made from prefabricated steel sections.The clarifier is fitted with a conventional skimmer mechanism. Finallythe compressors and other ancillary equipment are connected. Because ofthe small footprint these small plants can easily be housed in abuilding.

To further understand the distinct and diverse methods of waste watertreatment employing the novel apparatus provided herein, FIG. 13provides an exemplary block-flow diagram which can be used to identifythe various flow patterns and further understand the inter-relationshipof unit processes. FIG. 13 is divided into four areas, as delineated bythe broken lines. The bottom left area is a conventional preliminarytreatment area where the waste water is passed through a fine screen inunit A and is degritted in a hydroclone separator C. The screenings andgrit are deposited in a hopper B and sent to landfill.

The upper left area of FIG. 13 is the wastewater treatment and BNR partof the bio-reactor of the invention and represents certain exemplarycomponents thereof. Unit D represents a deoxygenation step orpre-denitrification step and references channel 40 channel 32 andrecycle 50 of FIG. 1. The unit D is agitated by the anoxic waste gasoriginating in lower zone 1 (channel 80 of FIG. 1. The line 301schematically represents the waste gas transfer from lower zone 1(channel 80) to upper zone 1 (channel 40) but in this aspect of theinvention the lower zone 1 is immediately below upper zone 1 and notransfer line is needed. Unit D receives raw influent (channel 30) fromunit C, recycle from head tank E and nitrified recycle from zone 2 (unitH). The purpose of unit D is to remove any useable molecular oxygen,accept nitrates from recycle and ammonia and BOD from the raw influent.

Unit E represents the head tank 16. This unit receives anoxic gas (309)from unit D which serves to mix the contents of head tank 16. Unit Ealso accepts raw waste water containing about 25 mg/L of ammonia and1.75 volumes of nitrated recycle containing no ammonia or appreciableBOD. After mixing, the nitrate in the 1.75 volumes of nitrated recycleare converted to nitrogen gas and the influent concentrations are thusdiluted by, e.g., 1 Q×25 mg/L ammonia+1.75×nil ammonia/2.75 Q=25/2.75=9mg/L ammonia and similarly 200/2.75=72 mg/L BOD. The denitrificationprocess liberates, e.g., about 2.6 mg oxygen/mg of nitrate denitrifiedand some of the alkalinity is recovered. These quantities are exemplaryand beneficial to the process. Denitrification is quite a fast reactionand is accomplished by the microbes naturally occurring in the wastewater.

Unit F receives, e.g., about 2.75 volumes of denitrified wastewatercontaining approximately 9 mg/L ammonia and 72 mg/L BOD. Since there isno molecular oxygen or bound oxygen, the biomass will become anaerobicand start using some of the proteins in the raw sewage to make aminoacids. The poly P microbes in the system will give up their phosphorusand load up on VFA's. There is some evidence that VFA's can be producedin anaerobic sewer lines where anaerobic slime is allowed to accumulateon the pipe wall. A rope like open weave tube (131) may be hung from thehead tank down inside the clean bore channel 12. There is minimal riskof plugging the channel because unlike other prior reactors there are noairlines or other pipes to become entangled with. It is to be expectedthat anaerobic biomass will accumulate on the rope and some VFA's willbe produced allowing some biological phosphorus to be removed.Monitoring the weight of the rope will give some indication of theamount of biomass present. The flexibility of the rope and the velocityof the water should cause excess biomass to fall off and drop into thechamber 67 sump where it can be removed as waste sludge.

Unit G represents the lower portion of zone 1. This area is highlyaerated and is designed to reaerate the anaerobic mixed liquor asquickly as possible. Since the mixed liquor that enters the lowerportion of zone 1 is rich in BOD, ammonia and sufficient VFA's, theoxygen demand in the lower portion of zone 1 will be the maximum for anypart of the reactor. The BOD removal step requires ammonia of cellsynthesis which is 5% of the BOD or about 4 mg/L. There is a feedforward stream of 2.75 Q which is transferred into zone 2 containingabout [9 in zone 1-4 consumed in cell synthesis]=5 mg/L of ammonia.Experience with vertical bio-reactors has shown that some of the ammoniais actually nitrified in the lower zone 1. It is not uncommon to find2-3 mg/L of nitrate in a bio-reactor designed not to nitrify. In thecase of a BNR plant designed to nitrify, some of the nitrifying bacteriawill end up in zone 1 because of the 1.75 Q recycle stream from zone 2to zone 1. Additionally there is 5 Q flow [containing 2 mg/L nitrate]from zone 1 to the deoxygenation Unit D. These flows will be denitrifiedfurther removing nitrogen from the system. Conservatively the effluentfrom zone 1 to zone 2 will contain no more than 5 mg/L BOD, 3 mg/Lammonia, and 2 mg/L nitrate. the 3 mg/L of ammonia will be fullyconverted to nitrate in zone 2. Therefore the effluent will end up beingabout <10 mg/L BOD, <10 mg/L TSS and <5 mg/L total Nitrogen.

Unit H represents head tank 15 and operates under very low loadingrates. The feed rate into zone 2 head tank is 2.75 Q containing 3 mg/Lammonia and 10 mg/LBOD. Zone 2 receives its air supply from zone 1(shown schematically as line 302). Because of the low BOD the biomassproduction will be low and the biomass produced by nitrification is ⅕-⅓that of BOD reduction. Because of the slow growth of nitrifyingbacteria, they cannot be permitted to be washed out of zone 2 in the1.75 recycle flow to zone 1. Fortunately these bacteria are attachmentmicrobes and will grow on any fixed or moving bed media. In the presentinvention moving bed media can advantageously be used, because the lowerend of zone 2 is designed not to allow any back-flow into zone1, andsimple screening will prevent the media from escaping at the top. Fixedmedia may also be employed but fixed media tends to plug up occasionallyand requires cleaning or changing. Moving bed media tends to beself-cleaning but does wear out over time.

Unit I is a conventional sedimentation clarifier which separates thebio-solids from the effluent and returns these biosolids [activatedsludge, RAS] to unit D or E. In a BNR plant the RAS should never becomeanoxic because the nitrate in the effluent and RAS will denitrifycausing the sludge to start floating in the clarifier. In the presentinvention there is the potential to provide an effluent from zone 2 witha high DO but a low oxygen demand, thereby preventing anoxic conditionsin the clarifier. Very high DO in the effluent is discouraged becausethere could be some resolubleizing of ammonia and phosphate in theclarifier.

Membrane separation, although expensive, eliminates many of theoperational problems of clarifiers in BNR plants. In the presentinvention membrane separation allows much higher MLSS and a smallerreactor. Membrane separation provides a better quality recycle waterthan the present standards require.

The upper right of FIG. 13 is the final chemical treatment of tertiarywater to meet recycle quality standards. By current law, chemicalflocculation, filtration and residual chlorine must be used. Unit M is aflocculating tank with mechanical mixer. Unit N is a rotating cloth diskfilter. Unit P is a ultra violet disinfection channel and combined backwash tank. Unit O is a chlorination step where just enough chlorine isadded to maintain a residue in the pipe line. Unit Q is a back wash pumpwhich can be used to backwash the cloth filter or the membranes ifrequired.

The lower right of FIG. 13 is the thermophilic aerobic digestion sectionof the plant. Unit R represents the first aerobic stage (zone 1) of thetwo step process. Unit S represents the second stage of the digestion orzone 2. These two zones are connected through an air lock valve. Unit Wrepresents the acid flotation thickening step. Unit T is an acid feeder.Unit V represents the dewatering step, in this case a centrifuge, with aunit polymer feeder U.

The BNR process above has been examined in detail in FIG. 13 in order toillustrate process advantages that are not reported in previousbioreactor designs. Among these novel process advantages are thatscreened and degritted influent is fed into deoxygenating channel 40 andis mixed with denitrified liquor from head tank 16. The head tank 16 isagitated with anoxic gas produced in channel 40 and with DO<0.05.Denitrified liquor from head tank 16 descends in channel 12 under anoxicor optionally anaerobic conditions completing the denitrificationprocess or optionally creating VFA's.

In addition, it is notable that downflow in channel 12 enters the bottomof zone 1 in the vicinity of the aeration distributor in an area ofvigorous mixing. Channel 80 which is the major portion of zone 1 ishighly aerobic, removes the BOD, rapidly oxidizes the VFA's consumingphosphorus and in some cases nitrifies a portion of the ammonia.

Further notable is the fact that rising liquor in channel 80 splits intothe deoxygenation area and a portion passes upward into zone 2. Zone 2substantially degrades the remainder of the BOD and converts theremainder of the ammonia to nitrate.

In additional aspects, waste gas from channel 80 circulates viadeoxygenation channels 32 and 40 and also provides the oxygen forbio-oxidation of BOD and ammonia in zone 2.

Also noted, a portion of nitrified liquor can be returned to thedenitrification step where the nitrate-N is converted to nitrogen gaswhile a second portion goes to a clarification step where the biomass isseparated from the effluent. The biomass is returned to thedenitrification step and the clarified effluent is discharged.

In related embodiments, anoxic gas is used for mixing anoxic liquor.Unit D deoxygenates not only the various liquid streams, but the gasstream passing through the unit. This deoxygenated gas can be usedsubsequently to mix the contents of the denitrification unit E. Thiseliminates the need for mechanical mixers saving energy, maintenance andcapital.

Additional embodiments of the invention provided novel anaerobicprocesses. Unit F is a long vertical channel which may converted to ananaerobic chamber for the purpose of creating VFA's. In the presentinvention there are no airlines or extraction lines in unit F. Thisallows the use of media such as open weave rope or tubes to be suspendedin the reactor without the fear of plugging the channel or becomingentwined with other pipes. The purpose of the fixed media is toaccumulate attached growth anaerobic bacteria (acid formers). The amountof fixed media and anaerobic biomass can be adjusted from the surface byrolling up a portion of the rope or fabric tube. The amount of media canbe monitored on line by measuring the weight of the rope. The liquidvelocity downward in channel 12 keeps excess biomass from forming andany excess will fall off. Since channel 12 is open at the bottom wasteanaerobic biomass would collect in sump 67 and be removed th flotationtank Unit J.

In still additional embodiments, wasting sludge through an air line 66or 69 provides instant spontaneous flotation upon depressurization.Wasting sludge [WAS] from a well aerated and mixed part of zone 1, aprocess not contemplated in previous designs, favours the capture ofphosphate in the sludge. Float solids are suitable for digestion withoutany further thickening.

Although the foregoing invention has been described in detail by way ofexample for purposes of clarity of understanding, it will be apparent tothe artisan that certain changes and modifications are comprehended bythe disclosure and may be practiced without undue experimentation withinthe scope of the invention which is described herein by way ofillustration not limitation. All publications, patents, and patentapplications cited herein are hereby incorporated by reference in theirentirety for all purposes.

1.-66. (canceled)
 67. An improved waste water treatment processutilizing a long vertical shaft bio-reactor comprising simultaneouslydiverting a predetermined fraction of oxygen-containing gas rising in aprimary upflow channel of said bio-reactor into one or more superiorupflow channels, and simultaneously diverting a different fraction oftotal fluid flow into one or more of said superior upflow channels,wherein non-plugging flow in said primary upflow channel is achievedwithout the use of orifice plates.
 68. The improved waste watertreatment process of claim 67, wherein flow velocities in said primaryupflow channel can be effectively adjusted to as low as 0.25 ft./sec.69. The improved waste water treatment process of claim 67, furthercomprising recycling of degassed liquid and/or raw influent in a firsttreatment zone of the bio-reactor to allow deoxygenation withoutmechanical mixing.
 70. The improved waste water treatment process ofclaim 67, further comprising recycling of degassed liquid and/or rawinfluent in a first treatment zone of the bio-reactor to allowdenitrification without mechanical mixing.
 71. The improved waste watertreatment process of claim 67, further comprising maintaining anaeration rate between about 0.2-0.5 mg/L DO without changing residencetime in said primary upflow channel of the bio-reactor.
 72. An improvedmethod for constructing a vertical shaft bioreactor comprising the stepsof: placing a cylindrical reactor housing defining an inner reactor wallinto an excavated reactor site, inserting a modular reactor componenthaving a central conduit surrounded by one or more channel-formingradial partition(s) within said cylindrical housing, said modularreactor component being deformed during insertion to displace saidradial partition(s) away from said inner wall by expanding a diameter ofsaid central conduit in a direction generally perpendicular to saidradial partition(s); relaxing deformation of said modular reactorcomponent to bring said radial partition(s) in proximity to said innerwall.
 73. The method for constructing a vertical shaft bioreactoraccording to claim 72, wherein said central conduit is expandedmechanically by a spreader sized and dimensioned for insertion withinthe central conduit.
 74. The method for constructing a vertical shaftbioreactor according to claim 73, wherein the spreader has paired,opposed and reciprocating spreader parts which can be manually,reciprocatingly repositioned between relaxed and expandedconfigurations.